I have both the TT .46 pro and the Evolution trainer .45 that came on my Alpha 40 (RIP). I love the TT .46. It is dependable, and easy to start. The Evolution can be a little harder to start, but it is also a reliable engine. I've never removed the limiters, as has been suggested, and I've never really had a problem. If I had to choose, I would but a Thunder Tiger engine over any other brand, but thats my opinion, I have only been in this hobby for three years so I don't have as much experience as some of the people who have responded to this post.