This is a superb combined OAG and filter drawer, extremely rigid, no light leaks and a nice large prism that completely illuminates an SC2210 (ASI220MM) sensor giving loads of stars.

There is a wrinkle with this though: for standard 55mm backfocus setups, the OAG is NOT compatible with T2-attachment guide cameras despite the presence of T2 threads on the prism stalk. The focal plane of the prism is deep inside the stalk, so it absolutely requires a camera with a long 1.25" body that can position the sensor as close as possible, such as the ZWO guide cameras. Attempting to adapt a T2-threaded design probably won't work unless you also add spacers ahead of the imaging camera to push the focal plane outwards, but this then means your 55mm distance is lost so compatibility with focal reducers will suffer. This isn't strictly Antlia's fault as it's a consequence of 55mm backfocus as a standard, but worth knowing if like me you waste a lot of time struggling to understand why your guide camera sees nothing but defocused blur.

One other small concern that is easily rectified: the adhesive Antlia use to hold the magnets in place for the filter drawers is not thermally stable, so it 'runs' a little over time. Not anywhere near the optical surfaces or filters, just a little over the magnets themselves so that the drawer 'sticks' a tiny bit when inserting and removing. This is easily solved with a bit of IPA and a q-tip, but something to be aware of when taking delivery. Also, the prism stalk is most stable when it's snug against the unit so consider that the default, and if you must raise it upwards for some reason try to install some support like foam or rubber rings so it doesn't tip after a meridian flip etc.

In general though, this is the best unit of this type I've used and beats all the 'combined' versions like Askar M54 due to being both lighter and shorter optically. Hitting 55mm by default is also a HUGE help when assembling your optical train, cutting down on three or four sensitive sub-mm measurements, and the ability to place the guide camera upstream of the filter is a big advantage for guiding narrowband.

This feels like a substantial piece of kit. Handy thickness of 37.5mm means that perfect backfocus was achieved just attaching it to my ASI2600 camera (which already has 17.5mm). I set it up during the day time and then fin tuned on the first clear night. Lots of accessories included and the filter drawer has a good strong magnet to keep it closed, so no risk of it dropping to the ground. The large prism meant I had plenty of stars to choose from with my ZWO 290 mini camera. No vignetting when the prism was fully in, even with my APSC sized main camera sensor. I use a ZWO AM5 harmonic drive mount, so regularly get good guiding at approx 0.8rms. With the OAG this improved further to approx 0.5rms. Really impressed with it.