If you mean the stock-standard in the finder holder type, I rate them average.
If you take one and further modify and improve, then I rate them excellent. I get 20 and 30 minute subs out of my system using one without any difficulty. ZERO flex (solid rings, threaded connections), and I get as many guidestars as I want using a Lodestar.
I modified a standard finder by custom solid rings (the tube is held by a VERY thin layer of felt and 6 grub screws), a custom non-rotating helical focuser, and a Prostar mini vixen clamp. As I mentioned, ZERO flex, any guidestar, focusable, detachable and light. Never had any issue with 20 or 30 minute exposures. Plus I painted mine to match
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