Kudos to Marc for such an excellent write-up and graphic method of showing what's happening at the focal plane.
(Marc: an extended version would be worthy of a piece in Aust Sky & Tel)
One thing that was not touched on was the quality of the optic. Many instruments are built to a price, rather than specification.
While good value for money optics are out there, I'd pick a smaller high quality instrument over a rubbish light bucket any day...as even the ancient Romans would say: Caveat Emptor !