Well , my combiner arrived a few days ago from China.
I chose the set without the 1st mirror attached. Quality wasn’t too bad, the hole for the red laser was a little sloppy +0.3mm, but a single layer of tape fixed that.
I did manage to squeeze it in before the first mirror and that made setting up really quite easy. Setting the height with shims was the best way rather than trying to adjust and tighten the screws.
I set the angle between the combiner mount and the 1st mirror to 90 deg with a square and that gave me a good starting point. Set the red laser focus to the longest distance and then fitted it to the stand. Not a great adjustment method, but does the job. I did a standard optical alignment on the CO2 laser first because the slight refraction through the combiner shifted it off. When that was back to normal I did the same with the red laser. In all it took probably 3 hours start to finish. The red dot is of course perfectly aligned with the laser beam and the same size roughly so as accurate as you need. Happy with the result and may even make general maintenance alignment easier.
The dot looks huge in the photo, but in reality it is very tiny.
Thanks for all the messages in this thread, it really started an interesting conversation.
Cheers
David