The Magnum .61 is a decent cheap engine. The Thunder Tiger .61 is a better engine, and probably the best value in RC engines today, but it does cost more. The TT will be more reliable, easier to tune, and will make more power. It's a better beginner's engine simply because it is more likely to be reliable straight out of the box. Some Magnums are as reliable as anything else out there, and some have air leaks that will drive you nuts if you don't have the experience to find them and fix them. Myself, I'd keep an eye out in the classifieds for a used TT or OS .61 or .65 if you need to save money.