Working at an incline involves more than just keeping up with belt speed or maintaining balance. There is much more effort being exerted due to having to work up hill.

As far as being a "lazy man's" way to work a dog I wouldn't go as far to call mill work or any sort of work lazy simply because it is a cheap way to discredit one persons method while touting your own. Each can be as involved and disassociated as the person wishes. Its simple to strap a dog to a jenny and just there drinking a beer while listening to music. Someone can also put a dog on an emill and stay with it giving encouragement along the way. Neither is any better than the other, different strokes.

Personally I find the emill far more effective and a much safer alternative to handwalking and no longer perform any road work aside from a bit of weight pull/chain drag.

With an emill I can get 4-10 miles of constant walking uphill out of a dog without any interruptions or risks of the animal stepping on or ingesting foreign objects, being hassled by strange animals or running into any nosey people.