I have been looking at these machines too. They look fascinating. My brother does some leatherworking as a hobby and he is intrigued by these machines. He told me that because of the way lower arm is built it would be perfect for all sorts of stitching in tight places.
There are many videos on YouTube showing operation of these machines, as well as reviews of certain machines. YouTube also has videos showing how to clean up, deburr, and tune up these machines. Folks have also posted videos showing how they added a motor to their machine.
If I buy one I will go through it to remove all sharp edges except for any that need to remain sharp. Make the machine look well used even though it isn't. After watching several videos it looks like this is a necessary step that needs to be done in order to make the machine perform flawlessly. I will also be adding a motor.
I already have a very nice sewing machine that does pretty much everything the average non-commercial would want. And it does it fast. But it weighs a ton and I hate to drag it out. I also have a Singer Featherweight machine. It weighs 11 pounds. Link:
https://en.wikipedia.org/wiki/Singer_Featherweight . I bought it at a garage sale for 5 or 10 bucks. I bought it just because I wanted to tinker with it. Someone had messed with it before I bought it and it was way out of adjustment. But I was able to get it cleaned up, timed, and running well without much effort. The leather sewing machine you are asking about is a much simpler machine so it ought to be fairly simple to tune one up and make it run great.
If I do buy one I will add a motor for it first thing. There are YouTube videos showing how to do this too.
Eric