OFTEN NOT! But once bought, you're stuck with them...
The main problem (as I see it) is the internal clearance. If you have a supplier that guarantees the internal clearance (c-3, c-4 or whatever), they could work well. With many suppliers (or 're-sellers'), it's hit & miss. I bought ~ 8 Boca's before I found one that actually ran well in my Shuriken. My attempt to fit them to my buddies pattern engine was a complete failure. Hardly an efficient way to spend one's money...
p.s. I was in Moscow years ago with Sergei Kostin, rebuilding one of his F2A engines. I noted Sergei removing ceramic balls & replacing them with steel ones. I asked why. Sergei claimed (at the time) that the only difference was the amount of 'noise' the engine produced... HMmm! As far as I know, the top F2A Speed Engines are not yet using ceramic bearings even though a lot of material out there indicates they ought to be better...
p.p.s. So far attempts to change to ceramic bearings in a Moki .15 (Clown) motor, K&B TQR motor, Nelson .40 Pylon motor, & a 1.20 Pattern motor all seem to have failed.
p.p.p.s Bill Hughes has reported that one of his F2A profi .15's was ruined when his ceramic balls "turned to dust" during a run...OUCH!