Tens or Estim

I'm considering buying a Tens or E-stim machine for the house. I've had success with pain relief and injury rehab with it at the PT office, but thought it would be great to have one at home. They aren't that expensive, but I'm not sure which kind to get. Anyone have experience or suggestions? Here's one I'm considering:

http://www.protherapysupplies.com/pd_digital_4_channel.cfm/>