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A dob is fine for astrophotography, provided you add a rotator, this would likely be combined with some motors for a given mount to keep it pointed at the same object in the sky, essentially a tracking dob mount has the night sky appear to rotate, and the rotator cancels that out, something like an onstep controller is not a bad thing to keep in mind for an aftermarket tracking option.
The issue was not with focal length, more the F ratio which is focal length / apeture size, as they are the same focal length, the 10" is faster, so it takes images in a shorter time, at the trade off for a bit more need for a coma corrector if thats your preference, (not as big an issue with visual), and a slightly smaller ideal focus window, (again not as big an issue with visual)
This is kind of just a principle of all telescopes, the higher the F ratio, the slower / darker things are, but the more relaxed focusing it is, at F/4.7 with the 10" guy its not an issue, sorry if I went driving you down the wrong trail, as most newtonions are about F/5
A smaller refector can work, certainly more portable, however for larger magnifications, a large apeture is king, e,g, if you want to do planetary, for deep sky, either work, just the higher the F ratio, the longer it takes for the same image brightness,
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