[woodcote]

These drop arm lathes are rubbish when used to true two tyres at a time.
None of the brands, even the RSM when using the ball race 2nd arm, ever lower exactly parallel, and you never get equal loading on both tyres.
The claw mounts don't help with accurate/parallel seating of the two bushes anyway, it's just a limitation of the concept.

Usually I true on the slightly downward leaning side, as this naturally puts a slight camber onto the outside of the tyre, and provided better hook up[ and bite when you load the tyre up into the corner. Then you switch the axle around. You can mark the handle you turn on the lathe, to try and get both tyres the same diameter, but really, you also need to check them with a good set of digital calipers.

I got to try the German version (RSM?) and was really disappointed that it didn’t true both tyres flat - therefore loading one tyre more than the other (potentially damaging that tyre). I’d thought that was the point of the tool - truing tyres on plastic wheels on the axle. I chose not to spend £150 + postage and stuck with my DIY truer - despite its deficiencies, it did a better job for what I needed...