Model 647
I'm looking at one also, for much the same reasons you list. I think they will be one those "grail guns" in 10 years and everybody will want one. Remember, almost all the current grail guns were models which really didn't gain much traction when they were marketed. Model 58's come immediately to mind as nobody much cared for them when they were available.
I've heard it both ways on the accuracy department. From one I can gather it is either gun specific or one type of ammo works much better than others. Having owned 17's in the past, they are extremely sensitive to bore fouling and in order to get good results, diligent cleaning practices must be followed. Rick Jamison wrote on article about it in "Shooting" magazine when they first came out and his produced outstanding accuracy. I think they would be a very cool 50 yard gopher gun, if good accuracy can be maintained. The one I am looking at shows decent workmanship and a neat feature regarding the extractor machining. If it only didn't have the d@%&ed lock!
I kind of view it as a poor man's version of a Jet...which come to think didn't have a positive following in the day either. Just try to find a cheap one now.