based on the questions you are asking, please take the following advice into consideration.
buy the poison. price is a factor, otherwise you wouldn't be asking. several people have already commented that the bk2 and the poison are very similar in performance. that solves that problem.
http://www.seyberts.com/catalog/Jump/Break_Cues-332.html
If for some reason you don't like it, you shouldn't have a tough time reselling it.
the saying, "It's the indian, and not the arrow" most likely applies here.
best of luck.
now, playing devil's advocate....
If you break hard and have a tough time hitting center ball, then you want a very low deflection break cue. this is where the bk2 excels. the 314 shaft deflects very little and will provide more accuracy assuming you're following the "whack the crap out of it without control" method.
again, the bk2 does not jump very well. no low deflection shaft does.
If you got a used, wrapless bk2 for $200ish and a used poison jump for $90ish, then I don't think you would be going wrong that route either.
then you have to ask yourself if you want to and can carry the extra (jump) cue in your current case. And do you want to pull out the jump cue for a shot, or would you rather just break down your break/jump cue.
with a sound breaking technique, you will be very well off with either cue.
heck, you could buy a poison break jump and a breakrak deluxe for the same price as a bk2 and a jump cue.
hopefully this is enough input to help you make the best decision.
oh, btw, if you're really really good, then get the pink breast cancer awareness poison. It will intimidate your opponents immensely, and support a good cause, IMO.