If you mean one of these:
http://www.nitroplanes.com/blex332c404c.html
Make sure that you do everything you can to avoid adding unnecessary weight.
I put a 2C .46 Tower Hobbies engine into one and it flies pretty well. No problems with verticals.
You have to experiment with the C.G. if you do not want the nose to drop in turns, although I'm quite used to this with all of my biplanes, so I normally correct w/o thinking.
The C.G. placement is a bit touchy, moving it .5 " back or forward makes a big difference so be careful.
If I recall correctly the thrust angle needs a bit of adjustment as it comes. I recall that it had too much down thrust and maybe not enough right thrust.
Once "dialed in" it's a good flyer.
I really haven't had problems with uncommanded snaps, as I never let it slow down that much on turns into final.
Like most highly acrobatic planes, it is designed to snap quickly.
If you are not used to this, it may catch you unawares.
I'd suggest keeping it high in the air until you are comfortable with the way it flies. Likewise make longer approaches straight in until you know how it will react, especially in cross winds.
It's not a "difficult" flyer, but you'll want at least 20% expo on low rates and about 45% on high rates ( over 50% makes no sense on many planes.... ) to keep it from seeming twitchy, due to the excellent response. It rolls very quickly.
It's not a "dog" by any stretch of the imagination, but a .70 4C engine may produce too little power for this plane depending upon the output of the engine. e.g. the cheaper OS .70 sized 4C will definitely produce an anemic performing plane IMHO.
The finish and build is excellent ( re-enforce with thinned epoxy and CA everywhere you see wood ) but I wish CMP had used CF landing gear on this plane like they did on the Giles 202 .50 ver. 2.0. Not a huge problem though.
The hinges use pin hinges instead of CA hinges, and are both pre-drilled and slotted very well. Installing the control surfaces is trivial because of this.
The only hardware I changed was the tail wheel gear, for which I substituted a much better $2.00 cost, assembly which you can order from Tower as a part for the GP Ultimate and other planes.
Other than the engine mount and tail, I actually used the provided hardware and haven't had any problems with it.
Standard sized ( cheap SG5010 ) HiTorque servos all around on mine.
That's all I recall off hand.