I too would like a recommendation. I recently broke my right scaphoid (wrist). Unfortunately this break came back to back with a recovery period for an operation on my opposite wrist (yes - I'm in the wars) and after 4 months of atrophy my arms are now in terrible shape. While I spend hopefully my last month in plasters I'd really like some sort of arm work out that won't endanger the bone recovery in my wrist.
If you are interested in EMS or interested in 'muscle memory' then check this abstract out:
If there aren't any machines on the market that can do a simultanious crossed electrode stimulation it seems clear that there should be. Maybe an electrician friend of mine may help me modify an EMS machine to do this. Meanwhile, what machine is worth investing in?