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The Orion TOAG has a narrower profile (15 vs 16.5 mm) which can be important if backfocus is tight. It also has an adjustable prism position, whereas the ZWO is fixed. As a trade-off, the ZWO one looks to be a little more robust. I've only used the Orion one, for 3 years, and it's still performing superbly, FWIW.
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