Do you drive a car or SUV? Pretty sure that your automobile engine uses plain bearings on the crankshaft and cam(s) shaft.

The typical beginner would be better off not buying engines with ball bearings. Ball bearings require gentle treatment, while most beginners tend to land nose down or off field too often. Dirt is very hard on ball bearings, while bushings tend to flush it out the front.

OS engines tend toward milder timing, which makes them easy to tune and run. The LA series is even milder, which means they produce slightly lower power but are very user friendly. If you don't like the power they make, you should experiment with props a bit more.