This appears to be well made, if rather expensive, but sadly it didn't fit the polar scope in my EQ5 mount, so I had to return it. I measured the internal diameter of the adaptor, and I made it 29.82mm - it would need to be 30mm for my polar scope.

I bought this to use with the skyguider pro to help with polar alignment and avoid crouching and back pain. Unfortunately it’s almost impossible to achieve any focus of the retinal. I’d say the collar is difficult to fit as after the first time the brass banding bends out of groove. Also the 1x is too small and the 2x with the collar you can’t achieve focus.

Bought this in the hope that it would fit the polarscope of the Skywatcher Star-Adventurer - and it does. Pretty expensive for what it does but cheaper than some alternatives. Whilst not having had the opportunity to try it out with my OTA still awaiting shipment, it is pretty obvious what it’s benefits are; particularly at higher latitudes.