+ 1 for the thread. Good discussion going on.
Atlas mills are small and lightweight. This one looks very cared for in the photo you posted. These aren't the 4000# bemouths that industry used to build naval vessels and steam locomotives, by any means. However, oh so perfect for small, one off part runs. They were designed for hobby work, so generally don't have extensive wear and tear of the big iron. Also tooling is generally cheaper than bigger mills, because it is smaller. although collets and arbors, as well as horizontal shell mill cutters are definitely becoming scarer, and hence going up in price. So both plus and minuses.
Look on line for an old digitized version of Rudy Kompkoff's horizontal milling machining video. He used an Atlas to do all sorts of amazing things. If you would enjoy practising yesteryear machining, buy it and go for it! the Atlas would be a perfect addition to your shop as it takes up very little floor space, yet will do some surprising processes.
One thing to do, definitely ask about accompanying tooling and make sure the price is reasonable. And Let us know what you decide!
Glenn