I've got 8 or so of the version Mole Valley sell and they are great. Not as good as the Granpas ones probably but I've got a lot of pens! Takes a whole 20kg bag. I site mine on paving slabs which makes it work better. Rat population definitely much smaller now and crows etc can't use them.
As for training, I put a flat stone on for a couple days so they get to know it's the feeder and then take it off. Once one gets it, they all do. Funny watching them at first gently putting a foot on the treadle and then taking it off again. Only real issue I had were my leghorns who exploded into the air every time it made a noise. Took them about a week but they are there as well now.
Other issues would be spilt feed getting under the mesh treadle where they can't get it so I'm thinking of siting it on a raised mesh that they can get under so any spillage will be hoovered up. Also, the MVF ones are not totally waterproof on the seams but I have siliconed them inside. Plus they are quite tall which may be a problem in strong wind. I believe the Granpas ones are flatter.
But I would totally recommend the treadle concept and would probably invest in the best if I only wanted one.