Better late than never I guess. I have 3 Union Lockstitch machines and 3 Campbell/ Randall machines. The parts never were an interchangeable problem between the early Randall and the later Campbells that I have.
The Unions most definitely do a tighter stitch than do the Randall/ Campbells but as was noted one must speak carefully to them over time. My experience has been that any problems I have encountered have just made me understand them a lot better. There is no comparison between the stitch pattern of these machines and jacked up Chinese machines or any different feed machines. Needle awl just works for us here big time. If there is any doubt then one must be aware that the LARGE holster companies use these almost exclusively in their factories and as they have access and funds, that must be telling something.
Still wonder what these are like though............