Andrew, the answer is easy from my perspective. I've never used a Union Lock, some people love them when they're sewing good. Some people hate them and don't get along with them at all. I suppose you could say that about anything including a 16. I have two Landis 16 and love em. I use them for making saddles and tack, they sew tight.
Besides there's a fella who has been rebuilding the landis 16's. He advertizes in the shop talk and or leather crafter journal. His name is Eli ....? No sure his last name, very helpful and knowledgeable. He has parts. If I can help just PM me a message.
Bob