Ok so I just read the wiki on this, and don't want to wade through all fifteen pages of this thread, but I have a question:
is there a reason it's only 1x2 room?
is it worth creating a larger room in a hallway for training anyone who walks through?
The 1x2 room is the most effective for a small amount of items. As the size of the room increases, so to do the number of items inside the Coinstar(TM) need to increase. The 1x2 room also is small enough to build and get ready faster.
I use a 2x3 room, with 1000+ coins, that way I can station my 2-dwarf squads and they will have enough room to both stand in separate squares and be trained at a roughly-equal pace. This only takes half a season to get Legendary Armor User from Dabbling. The small room also reduces the amount of travel a flying dwarf has, and (if I'm wrong, feel free to correct me) minimizes the danger of impacting the wall at terminal velocity, killing a recruit.
The main (and deadly) danger of building this into a commonly-traversed area is that Urist McDumbass will at some point drop a XXPig Tail SockXX in the Coinstar and as the items fly about, the XXPig Tail SockXX will cave in heads and shatter bones like no ones business, killing and maiming indiscriminately as the worn out sock gains more kills than your most salty military dwarf.
This is why I use the mine cart repeater shown earlier in the thread, and use its built-in off switch when a problem arises. It also helps to have your militadwarves replace all their clothing with armor, so they aren't a victim of their own stupidity.