It's SL 1, so even something targeting only casters (preventing abilities that take "patience and concentration" is something barbarians do to *themselves*, and it matters so little people often forget), with will save negates has even odds of working; A wizard has a will save of about +3, while the DC will be 14-16. The concentration check DC of 20+SL means that target concentration will rise faster than the DC will, since *max* SL goes up 1 every two levels (and casters can cast below their max SL), and concentration goes up around 1.2 per level, since casting ability score goes up, too. Concentration checks start with a decent chance of stopping spells (\~70% at level 1), and goes down around 5% per level.
But then, there's the opportunity cost standard. If the target might fail a will save, you might as well hit them with [Sleep](https://aonprd.com/SpellDisplay.aspx?ItemName=Sleep) or [Color Spray](https://aonprd.com/SpellDisplay.aspx?ItemName=Color%20Spray), which takes low-HD casters (or more importantly, non-casters, too) out of the fight for more than a round/level, and which prevents the target from moving. Since Incessant Buzzing only prevents casting *in its area*, and doesn't do anything to prevent moving, most casters will just move away and cast if there isn't also an ally in the area to AoO. Sleep is also much more generally useful (even if it doesn't work on elves or anything immune to \[mind-affecting\]) than something that basically only works on casters at very low levels when casters are pretty rare.
Not only can your hypothetical caster move out, the area is only 10 ft. in diameter. Even if you have an ally threatening them, they can always 5 foot step outside the area unless the positioning is such that an ally or wall is blocking the adjacent clear space.
Ah, whoops, I just skimmed "10-foot sphere", and assumed it had to mean radius like most others... Yeah, if you can't even stop a 5-foot step from leaving the area, you basically could only use this on someone already immobilized with other spells, which narrows the circumstances of use even more.
Honestly, if you already need to immobilize someone, and that relies on the enemy failing a save, you might as well make this spell a glamer and not have a save to disbelieve the sound and make it SR:no. Needing to take two actions and fail two saves (plus possibly beat SR twice) is a lot to ask to just make them make a concentration check they can still succeed. How often does the same enemy fail five rolls in a row, and if they do, why aren't they dead already?
It's a level 1 illusion spell. So.... yeah it's not supposed to be powerful. It appears unthreatening (It's a buzz. So what?), but it it's good at lower levels to cause casters to loose their spells, which at those levels is a massive blow considering how few of those they have.
Keep in mind Color Spray, *the* SL 1 save-or-die of choice for the discriminating CC caster, is a SL 1 illusion spell. Invisibility-granting spells start with Vanish at SL 1. Also, spells like Silent Image have power that is difficult to quantify, since doing something like making the illusion of a solid wall over a door can prevent someone not familiar with an area from even finding you, and I've often done things like have a team of NPCs use Ventriloquism with it to bait the party's paladin into stepping onto a pit trap attacking a mirage.
Meanwhile, the ability to just walk out of the AoE renders this spell pretty terrible.
It's SL 1, so even something targeting only casters (preventing abilities that take "patience and concentration" is something barbarians do to *themselves*, and it matters so little people often forget), with will save negates has even odds of working; A wizard has a will save of about +3, while the DC will be 14-16. The concentration check DC of 20+SL means that target concentration will rise faster than the DC will, since *max* SL goes up 1 every two levels (and casters can cast below their max SL), and concentration goes up around 1.2 per level, since casting ability score goes up, too. Concentration checks start with a decent chance of stopping spells (\~70% at level 1), and goes down around 5% per level. But then, there's the opportunity cost standard. If the target might fail a will save, you might as well hit them with [Sleep](https://aonprd.com/SpellDisplay.aspx?ItemName=Sleep) or [Color Spray](https://aonprd.com/SpellDisplay.aspx?ItemName=Color%20Spray), which takes low-HD casters (or more importantly, non-casters, too) out of the fight for more than a round/level, and which prevents the target from moving. Since Incessant Buzzing only prevents casting *in its area*, and doesn't do anything to prevent moving, most casters will just move away and cast if there isn't also an ally in the area to AoO. Sleep is also much more generally useful (even if it doesn't work on elves or anything immune to \[mind-affecting\]) than something that basically only works on casters at very low levels when casters are pretty rare.
Not only can your hypothetical caster move out, the area is only 10 ft. in diameter. Even if you have an ally threatening them, they can always 5 foot step outside the area unless the positioning is such that an ally or wall is blocking the adjacent clear space.
Ah, whoops, I just skimmed "10-foot sphere", and assumed it had to mean radius like most others... Yeah, if you can't even stop a 5-foot step from leaving the area, you basically could only use this on someone already immobilized with other spells, which narrows the circumstances of use even more. Honestly, if you already need to immobilize someone, and that relies on the enemy failing a save, you might as well make this spell a glamer and not have a save to disbelieve the sound and make it SR:no. Needing to take two actions and fail two saves (plus possibly beat SR twice) is a lot to ask to just make them make a concentration check they can still succeed. How often does the same enemy fail five rolls in a row, and if they do, why aren't they dead already?
It's will negates, only really useful against casters and only forces a concentration check. Not likely to actually do anything
It's a level 1 illusion spell. So.... yeah it's not supposed to be powerful. It appears unthreatening (It's a buzz. So what?), but it it's good at lower levels to cause casters to loose their spells, which at those levels is a massive blow considering how few of those they have.
So are colour spray, vanish, and silent image. There's no shortage of more effective will save or suck even at 1st level
Keep in mind Color Spray, *the* SL 1 save-or-die of choice for the discriminating CC caster, is a SL 1 illusion spell. Invisibility-granting spells start with Vanish at SL 1. Also, spells like Silent Image have power that is difficult to quantify, since doing something like making the illusion of a solid wall over a door can prevent someone not familiar with an area from even finding you, and I've often done things like have a team of NPCs use Ventriloquism with it to bait the party's paladin into stepping onto a pit trap attacking a mirage. Meanwhile, the ability to just walk out of the AoE renders this spell pretty terrible.
When you are looking at opportunity cost (this versus that) I can agree there are more attractive options.
The illusion of choice for mages who wish to inflict tinnitus on others