Got a BB chip fitted over a year ago when they were about 250 quid. Had cambelt and water pump changed and wanted it chipped to.
Produced 148 bhp with BMC CDA, Magnex inc Decat and chip. So about 11 bhp increase IF car came out of factory at 137 quoted bhp AND if I had not lost any power over years of use.
So other than any power increase, the other benefit is better drivability with power seeming to come in a bit earlier and things seem better all round.
But at todays prices I would not go for a chip unless it was a SMT6 or unichip as they are not much more than an ordinary chip now.