I own Saitos & Magnums, 3 of each. The Saitos are light, very light, and that's about the only difference I can see. Both will take a third of a gallon of castor blend fuel to break in properly, then you can switch to synthetic, if you like.

I recently broke in a Mag .52 for a buddy and I have its bigger brother, the Mag .61. Neither are powerhouses, but both run very reliably. Mags are just about exact copies of OSs. Their initial quality is not as good, necessitating a longer break-in, but afterwards, they seem to run the same. The Mag .91 is really a good engine.

The YS pattern fliers run a special fuel and special after engine run oil and mess with them a lot. Some people swear they don't touch theirs and those tend to run YS engines a lot and have done so for a good while. I tend to be a pour fuel in it and go fly type person, so I haven't bought one.

My last two 4-stroke purchases have been Magnums, the .91 and a .70. I haven't flown the .70, but it sure ran well on the bench.