I've fired standard Piranhas, a BBT by Tribal, and a more recent version of the Boo-Yaah' frame, if you're looking for a good electronic experience, you're gonna drop loads of cash, but the differences are notable.
Piranha Pro, pmi cradle, nitro, microline, 12v rev w x-board
This product gives quite a superior rate of fire and trigger pull to the prianha, and has several modes (see other reviews for details). It comes stock with a tourney lock, which restricst the frame to semi and safe modes. Mine has also had a SWEET trigger job on it, removing the extra mm or two pull, good for increasing rates of fire. The trigger guard is removable, however I don't plan on using this option. Also comes stock with a small rechargable battery and car charger, both of which are junk, so I discarded them. Problems after installation are easily fixable by a knowledgable store owner or airsmith, and are few and far between.
Some problems include the rechargable 9v battery and charger included in the base package, which are junk: you are better off just picking up a new duracel or energizer before you play. Another downside to the Boo-Yaah' is the fact that you have to remove your battery after play, as the frame never completely shuts down, so keeps pulling a small charge from the battery, a pain for people who play once a week, but easily solved with a bit of care. The butttons and innards are quite sensitive, and a fraction of a turn to one allen screw in the board from normal wear and tare can lead to a day of odd problems. The frame is set by 2 small set screws next to the seer, and must be perfect or the seer will not catch the hammer when recocking. Lastly, this frame is quite hard on the hammer, as a normal semi is not designed for such high rates of fire, however this problem is easy to spot and reativly inexpensive to fix.
A solid upgrade for those who can spare $200 to upgrade their current gun easier than $900 for a regular semi. If you have a considerate and reputable dealer, the problems should be a non-event, as someone with a working knowledge of markers and their internals should be able to spot them as they arise and direct you toward the fix.