Really depends on your style. I myself use the Aegis Covariants. Coupled with all my buffs and well...hard to punch through them. Granted if you want the full bonus of the Breen set you'll have to use them.
Thanks. I must've missed it but what is the bonus for collecting all three breen equipment? I have always used high hp shields. Not sure why. But I have several shield regen abilities so it seemed the right thing to do.
With the rapid fire transphasic torpedo, the breen set isn't an entirely bad deal. It could be good for an escort that specializes in transphasic torps because you get the boost to energy transfer and a free energy siphon (which can help out more than you think).
As for a science ship, it's already a very skill intensive build so you might miss those points you spend in transphasic. It CAN work for a build if you put your mind to it, but it would be rather specialized (not that there's anything wrong with that).
I could actually see a B'rel rocking this set pretty well. I hear transphais is popular with them because of their fire on cloak ability.