I am used to OS so that is what I buy but can't complain about TT either. I don't own one but have helped new flyers with theirs and the engines surprized me to find that they are just as easy to adjust and break in for reliable strong running as the OS (unlike the finicky ST engines). I prefer the OS remote needle valve to stay clear of the prop but the new TT engines have an angled valve so thats not much of an issue any more.