4u2nv, I bought and installed the Picco P2 .21 engine. It installed with no trouble at all, but the power level sucked. I was totally disappointed, so I started this thread:
https://www.rcnitrotalk.com/forum/showthread.php?s=&threadid=14516&perpage=15&pagenumber=1
It is well worth your time to read that thread.
After I did all the things in the above-referenced thread, the T-Maxx now runs like a raped ape. It is absolutely a blast to drive, much more fun than before. It wheelies on demand and screams like a banshee. The P2 is a great wake-up for the Maxx.
You will absolutely, positively have to buy a tuned pipe. The P2 is a dog with the stock T-Maxx pipe. Other than that, everything else should be OK, unless you really hammer the hell out of it. I did the FOC and a metal RRP spur gear, but you may not need that.
One thing to be very careful of; check the fit between the one-way bearing on the EZ start and the backplate of the engine. That area was binding on me. I actually sanded a little off the outside of the plastic gear that the one-way bearing sits in, and that gave me the clearance to make the starter work without the bearing grinding away the aluminum.
If you do it right, you will be most happy with the upgrade.