Don't really know about others' preferences, but I find it vexingly inconvenient when you try shooting powerups while (sometimes unknowingly) having a very limited number of their respective ammo, you end up powering up the ammo only with no amount gained. This forced the habit of depleting the last few bullets of it first before shooting which has occasionally put me in some disadvantageous situations. So, we don't we just consolidate that punishing behaviour into always getting that juicy +20 ammo no matter what. Isn't it a lot better that way?

P.S: The mutator running on ZD already does this by default, and everyone seemed quiet and content about it.

Stealing a conversation I had with Naps about this, without his permission 🤫:

Violet CLM: It's bad enough that if there's a powerup in the wall that you're supposed to destroy with electroblaster, and you have 5 ammo of that weapon already, your best move is to fire five bullets and then use the electroblaster.
NapsZ: yeah i am not fan of that mechanic either... i get that it's supposed to balance ammo gain in case you already have a powerup but i have a strong feeling arjan didn't thought about the situation of having less than 25 ammo
NapsZ: how would you do it if you were in his place? what should the result of destroying a powerup monitor that you already have ammo for? consistent +25 gain?
Violet CLM: okay I don't actually know how I'd do it to be fair
Violet CLM: Putting aside the inconsistency with special moves, the bullet 0/20 distinction does make some sense
Violet CLM: I think it's solving two problems:
1) If you shoot a second powerup monitor of a weapon you already have a powerup of, you don't want that to be useless. So okay, a flat +20.
2) If you have no ammo of a weapon and encounter a powerup, you don't want that to be useless either. So okay, 20.
Violet CLM: But it falls apart because the best possible move is to bring yourself down to zero and then shoot the powerup, and that's ridiculous.
Violet CLM: +20 for every powerup shoot is the simplest but it's not satisfying ig.
Violet CLM: You could change the "no ammo of a weapon" case to something smaller like +5. But that's bad for new players. They get a powerup, they want to try it out right away! Oh no all their bullets are gone now. Powerup over.

A new idea, while we're tossing them around, would be to set your ammo to a minimum of 20. So if you already have 33 or 46 or 50 ammo before shooting the powerup, you stay at 33 or 46 or 50. But if you have 0 or 5 or 19, your ammo changes to 20.

Aw, I liked that feature the way it is. Makes a player force depleting their ammo or use special moves on the PU.

I agree with Warren's suggestion here. I don't see why shooting a powerup should yield 0 (extra) ammo to a player in any case, while special moves can maximize it.