by "plain" you mean sleeve ?
they do work excellently,
HOW excellently depends on the materials, design, mfgn, etc.
the revised MCP600/ne 50Z have a large dia ceramic shaft with a grooved passageway down its length to promote fluid flow, but the impeller 'bearing' is the mere hole in the glass-filled acetal (Noryl ?)
- hardly the best bearing matl, but if the film is maintained then should last a long time
what is long ? who knows w/o testing
the sapphire on ceramic is interesting, know nothing about such
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