Just to be clear I'm not trying to sway you to a knee mill, simply pointing out that they are not necessarily out of the question for a small shop. Bench mills and even the dreaded round column mills are very capable. There is a poster on the forum (davidpbest) who has some strong arguments for the benefits of a bench mill vs the Bridgeport style mills mostly to do with the rigidity of the head.
I have a Sherline mini-mill which is a very small square column bench mill (50lbs), and a Clausing 8520 knee mill (900lbs). Both work well, but they are grapes and watermelons in trying to say one style or the other is superior.
Sherline on the Clausing
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