I think it is important to think about the Marc Pro device or ESTIM use for pitchers in the context of the changes & philosophies that have evolved regarding increasing velocity & pitcher training over the last 30 years.
I pitched in College & MILB ending in the mid 90's. At that point in time I, personally, was not aware of ANYONE actively using: Rubber Tubing, Weighted Balls, Flex Sticks, Box Jumps, Extreme Long Toss, Cleans & Olympic Lifts and or any real significant weight training. (as a training / recovery method for pitchers)
Most all of these methods are fairly mainstream now for a large cross section of elite pitchers.
What will science, technology and research bring us to the mainstream 30 years from now? Will pitching training and recovery look identical to today? Has everything been discovered and unlocked about velocity and arm care? Um, no!
If you were a Pro Pitching Coach back in the early 90's & suggested the above training methods you would have been unemployed in about 5 minutes. Now, 25 years later, if you do not incorporate many of the above methods you would also be unemployed in about 5 minutes. What does that tell you? It tells you that you must keep an open mind and do as much research as you can on a method, add a major dose of common sense and proceed accordingly. This is a must if you want to try to stay ahead of the curve and gain an edge.
I applied the above method to the Marc Pro issue. I ordered 1 early this week & my 2021 had it strapped on last night doing a global arm flush watching the Celtics beat GS after we threw long in the yard. Am I 100% positive that it will make him a better pitcher? No. Am I going to wait for 10 years of research to sift out a definitive answer? No. Do I think it will do him any harm? Quite the contrary. The increased blood flow and vascular dilation makes perfect sense to me as a layman on the medical aspect.