This just works. I have an ASI 533MM pro and a Samyang 135mm lens (Nikon, as I have a Nikon DSLR) and everything fit together fine. I've tried with a couple of filters and have had no issues achieving focus or with tilt.

4 stars rather than 5 stars because when I put everything together so that my camera is "the right way up" the filter draw points at a funny angle (maybe 45deg) towards the ground. That's very annoying. Luckily I can just rotate my camera/lens 90deg and have it mostly pointing up (there is no lock on the filter drawer so I want it mostly pointing up to avoid some horrible filter falling on floor situation), but if you had a different camera maybe this is more annoying. There's no obvious way to correct this.

This arrived recently from FLO and I’ve had a few days to test it. It is very solidly built and holds the lens securely. The M42 thread camera side works well with astrocams with a 17.5mm sensor depth and a 42mm thread and there is an adapter for larger. I did some daytime tests with my Nikon 180mm lens and an Altair Hypercam 26c that like some of the ZWO cams has that 17.5mm internal distance from the thread base to the sensor. In this case the adapter is perfectly calibrated and infinity focus is in the right place.

However, when a filter is inserted matters change. With the unit by itself you need to focus short of infinity as the adapter itself offers no adjustment to compensate for the thickness of the filter glass. On telephoto lenses this is likely to not be a problem. If you want to go to shorter focal lengths, especially for wide angle Milky Way shots, expect to have to add spacers up to 1/3 the filter thickness. This is no big deal.

A bigger issue is the lack of any aperture control for G class lenses. Other manufacturers of similar adapters either have a pin to hold the lens wide open or full adjustment. If your lens has an aperture control ring their is no problem, so the fully manual lenses from Samyang and Zeiss are fine, as is my older Nikon 180mm. Otherwise you will need to faff around with small (dental) rubber bands. E lenses can usually be fooled into holding a particular aperture by removing them from
A DSLR body where the aperture has been set to where you want it. I’d give this product 5* if it had aperture adjustment built in.