The Magnum XLS .46 will have a true ABC construction while the Thunder Tiger PRO .46 will have ABN. Both are fine engines. All of the OS LA series is JUNK IMO. Yes, there are problems with ACE/TT service these days...hopefully they will pull their head out soon Magnum offers great service when needed. To date I have only seen one new TT engine that I thought was below par and after running it, it turned out to be just fine. Parts support from ACE currently SUCKS!, so that could be a problem. Still, all in all, I would choose the TT...once broke-in and properly set-up they are very user-friendly. I guess I'm kinda biased towards TT as that is the only brand I own...2-GP.15's, 2-GP.25's, 4-PRO.36's, 1-GP.42, 10-PRO .46's and 2-FS.91's (and that's after selling some, too )...no, they aren't all in use currently...maybe someday though