Are there advantages of using a turntable for linear motion instead of the normal high strength gears?
There is only one set gear ratio and i think a little bit more friction.
I’m a big fan of the turntables, the demo robot I built last year used them like this.
How were you planning to use them for linear motion?
They are also a bit more solid than just using gears, though I barely ever use them.
I am considering to use them for either a chain bar or a dr4b
Probably the turntables can work very well if you take it apart and apply WD-40 to the areas where plastic rubs together.
EDIT//:
In my opinion, for a chainbar it can be a good idea, but for a dr4b it can be not-so worth it. Buuut you can prove me wrong 
In my time of working on pinball machines, you don’t use WD-40 for long term lubrication. It just gets sticky after time and makes it worse. Pure silicone spray or the white lithium grease would be better.
Thanks for the important advice, never knew that! I’ll keep that in mind for the future