On their own, HS50s aren't bad. Not amazing in the lower frequencies, but few 5" monitors are.
I have the HS80s and they are a little better in the bottom end, but not much. I'm starting to think that you really need a sub with the HS series. I was thinking of selling my HS80 though and getting a pair of B3031As... Reviews of the b30301as are great and if you ignore the Behringer name on them, then IMHO they are slightly better than the HS80s and cost over €150 less (per pair)!
I had a chance to A/B them against my HS80s, albeit in a different room, and I think I preferred the b30301as. Than again, I'm going to try to borrow them from my friend (he got the b3031as last week) and test them in my room. Really give them a work over and see about switching.
Anyways, if you want to get the most out of the HS50s, couple them with the Yamaha HS10w subwoofer. It really gives you a great spectrum reference and will give you better mixes.
Depends on how comfortable you or your room is with mixing with a sub though.
I tried and tested a pair of BX8As before (8" version of the BX5As) and all I found was that the bass was exhaggerated quite a bit. Good monitors if you do electronic / trance music, not great for anything else.
TBH, you can get great monitors for less money these days, but alot of their apparent "effect" on your music is how they respond in your room and more importantly, how you compensate for their effects. I've heard great mixes done with a pair of Rokit 6s and b3031as which are relatively cheap, but the mixer knew what they were doing and they know their room well.
I could give you a pair of €4000 monitors and a pair of €400 monitors, not tell you which was which, and you could prefer the €400 over the €4000 ones, or vice-versa. Monitor choice is very subjective and dependent on your mixing circumstances and room. It shouldn't be about snobbery or a "higer price = better" mentality.
My €0.02....

YMMV....