IMHO, all that has already been said is good, free advice. I own at least one of all the mentioned engines, and to date, have not had a problem with any of them, (just lucky, I guess)

The new generation DL50 is awesome, for the money. I just ordered #2 from DL USA, here in Texas. I have an old one in a Lanier 87" Extra that weighs almost 16.5#s. I am using a mejlik 22X8, still on break in fuel and the engine spins almost 8grand with unlimited vertical. We are only 800 feet above sea level at our flying field in San Antonio. When I first took this plane to the field, I let everyone just think it was a DA 50, since they look alike. Several that owned DA's made the comment, that they couldn't believe the power and response from this engine, and it wasn't broken in yet. They were really surprised to find out, it was a DL and cost half of the DA's price. Don't get me wrong, I love my DA and 3W engines, you get what you pay for most of the time, but the DL is truly amazing for the cost.

The XYZ 50 is really just 47cc's and doesn't even come close to the power of the DL and is much heavier than the DL as well.
I have a STL 45 from HC that puts out better power than the XYZ, so I bought a 52, but it doesn't seem to be as tight and strong as the 45. Of course, each engine is different, and some require allot of break-in before developing their full potential.

Bob at DLUSA said he should be getting a new shipment in Irving next Tuesday, so you may want to get yours ordered, before he runs out again. They do go fast, even at $390 each, with standoffs, muffler and ignition, what are you waiting for?

Good luck and welcome to gas.