I know they're supposed to reduce the enemies crew, and shut down subsystems. That sounds kinda nice in theory, but... how effective are they actually?

It depends.

I use BP3, and I noticed that if I use it against a persistently strong enemy, when I manage to kill one side of the shields, that side doesn't regenerate. Or, it stops shooting for the duration, or stops using special abilities.

In about 50% of the occasions, though, it does no appreciable effect.

And when using BP3 against "normal" enemies, those ships usually blow up before the shuttles even have a chance to board them.

So, if you ask me, I'd say that it's useful in about 25-33% of the situations and useless in the remaining 75-67%.

Of course, I'm talking about PvE. I don't PvP, but I guess that a human player will prioritze targetting the incoming shuttles to avoid the subsystem damage. And still, some heals will negate BP after it lands.

They work for pve on most occations...
for pvp ... dont even bother....FAW will pick the shuttles off as they spawn plus a single tac team 1 will counter it

on the contrary, they are quite useful in both PvE and PvP. In PvP though I usually launch the shuttles point blank, with a stick of mines or scorpions for cover. that increases the chance that at least one shuttle makes it through the inevitable FAW/CSV/TS screen. Sure this doesn't always work against hardcore PvPers, but it's not bad against less experienced ones.

I agree that they are rather pointless for PvP. That said, I would wager a 5 man team launching them might become a pain.

Generally I just chuckle when I even see them. Cannon fodder. Even if they do reach me, they have no real appreciable effect. A very poor mans SubNuc.

The effectiveness seems to vary a lot depending on the level of the ability. BP1 seems to be almost ineffective. It rarely seems to do anything and is not worth even taking.

Meanwhile BP3 almost always takes effect and can disable up to 3 subsystems. However, you are giving up a Commander Engineering power for it.

The only effective way I've used it in pvp is mainly 1v1 on my Orion Marauder. I'd fly past the target while hitting warp plasma 3, boarding party 2, and release my interceptors all at once. I'm also dropping plasma mines to help the proton mines the interceptors drop. It's a nice little combo, works well in PvE as well. Less effective in group pvp of course.

I programmed my ship's replicators to produce simple combat androids. They're cheap, efficient, and disposable.

What about Directed Energy Modulation?

I would also use DEM before I wasted a slot for boarding parties.