They’re all good to be about the same performance wise I’d imagine. The Sky Watcher and Sky Rover both use FPL-53 and I think the Sharp Star does as well but I haven’t looked.
With back focus for flattener, if he reducer has a 55mm back focus then your Canon should simply work with the M48 EOS adapter. Canon has a 44mm back focus and then the adapters are usually around 10mm as well.
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