As far as the mechanical advantage of the treadle hammer is concerned, like most things, there is no free lunch. I have the plans for the Clay Spencer Treadle Hammer and myself & my colleague (a mechanical engineer) examined the linkage system and came to the conclusion that they do not multiply the input force since the pivot is practically in the center of each link. That being said they still hit a xxxx of a lot harder than the armstrong hammer, so I guess it comes down to what you want to use the hammer for. If you want to do precise work, then the treadle hammer is probably your best bet, however if you are making billets & drawing out stock all of the time, then a mechanical power hammer is a good option. Or if you have a lot of money to spend ( or a very understanding wife) then get an air hammer and you can do it all.
Cheers,
Chad