I tried UC at last and they seem relatively strong, but I had two main annoying moment about them and Penumbra in general. 
1. Purging/Culling sleepers seems like an almost no drawback action. -25% happiness malus is nothing for AI and I guess it is even more nothingesque for good human players? 5 turns per sleeper is not a big enough enough ratio to make hacking for sleepers a positive investment. Ofc it sometimes works with UC when you stack hacking speed bonuses and can hack a system within 2-3 turns. But usually you need to start from afar to gain backdoor momentum and bypass defensive programms so it takes more than 5 turns for sure.
2. Pirates get lvl 2 detection too early. Which is painful, because outpacing detection with advanced cloacking techs is already a huge science investment. It doesn't hurt that much when they get lvl 1 detection around turn 25 because you can squeeze lvl2 cloacking in +/- 5 turns with some investmant but not that much. But when it comes to lvl3 cloacking you usually need like 10+ times the science you produce by that moment to get there.

I don't have a good workaround in mind for those and I'll be glad to read some tips that can make my games smoother.