I really don't think they are very good on anything other than phase ships. Normal high tech ships that can mount them have to spend most of their capacity blocking enemy fire with shields and firing their own inefficient weapons to overload enemy shields. The alpha damage is great on paper, until you remember you're also effectively doing alpha damage to your own shields/flux systems via the big spike in flux when you fire them. I think the AI is reasonably hesitant to use them because they constitute such a big risk: you have to get into very close range and there is a huge spike in your own flux. The player can usually manage this risk (although it's still very easy to make a mistake), but the AI is not really equipped to do that. I find that very frequently with something like AM blaster medusa, you commit in and dump all your flux to deal damage and the enemy is not dead, and now you are <400 range away from the enemy fleet on max flux. Reapers cost 0 flux to fire and have much better range, so they work much much better on most ships.
Phase ships are uniquely good at using AM blasters because they don't depend on shields (and thus flux capacity) to block damage, and they frequently have the ability to bypass enemy shields meaning they get to spend the majority of their capacity on dealing hull and armor damage.
TBH, I don't mind existing AM blaster being in the game for phase ships, but there should be another option for other ships that want a similar type of weapon. I also personally think that phase ships are OP and need the nerf bat, but that's for another thread.