I have tried one of these engine.
I bought it to replace my 3 port sirio, and was disappointed at the performance. it is faster than RTR Engine but much slower than race engine. and my sirio wasn't even modified engine. So I sent my engine to RBMODS and currently waiting for it. Hopefully he can make it scream. I'll let know the result if you want.
If he can make it fast as or faster than my sirio, it is still a good value after mod $$$. Cause i paid $149 for engine + RD Turbo II pipe. Plus $69 for mod. I still pay less than Brand new sirio with new pipe. So We'll see.