All the plastic does is keep the balls spaced evenly- - - -it carries no load. As long as the bearing is packed and torqued properly, it doesn't matter what material the spacer is, and the assembly and torque procedures should be identical. I've used that type of bearing often with no issues.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!