I think this Marc Pro thing is just an e-stim machine. I'm not sure, I haven't done much research, but if that is what it is, I got one when I was playing for like $50. There are many brands out there. A lot of pitchers when I was playing would use the e-stim under the ice. I just liked it by itself. It felt like a massage which I liked when I was sore. I shot this vid in early 2010. Excuse the camera quality as I was still learning how to make nice videos. There is an affiliate link in the video but I don't mean to post it to get you to buy one, just thought it was relevant to the topic and would help some of you out. Plus there are probably newer models available. So do your research and consult a doctor before using one. https://www.youtube.com/watch?v=kWDTRUohfmo
What you are describing is a TENS unit. An e-stim unit is used to stimulate the nerves. This blocks pain and has it's uses for pitchers, but the Marc Pro is an ems unit which stimulated muscles, not nerves. For example, someone with back pain would get a lot of use out of a TENS unit, but wouldn't have much use for an ems unit. For a pitcher, on the other hand, we're actually looking to increase bloodflow through the muscle and to apply controlled retraction and expantion of the muscle.Here's a link to a TENS unit review site which explains the difference.