Interesting, indeed. It's similar to a MSEM, with the exception that MSEM is much lower in volume usually and it's geared towards heavy weights.
Well its kind of similar but different overall goals, its VERY similar to the rest pause/dc style training, but still different in its own ways. One of the best things about myo reps, rest pause, etc. is the work you get in the range that is so beneficial to progress and hypertrophy, and how easy it is to make constant progress in your training.
I use myo reps alot, even with relatively green trainees, when they are on the verge of a plateau, to be able to break their previous set/rep pr. Beginners make great linear progress with 3x5, 4x8, etc., but many times, when the 3x5/etc. plateaus, I will add a couple of myo-rep style reps at the end of their last set, which still gives them a pr and some very beneficial extra work. The more seasoned the athlete the more they tend to benefit from this style of training in my experience, beginners dont need to use these techniques nearly as frequently but they can still have their place in their training if used at the right times.
The thing that matters most over time is progressive resistance, beating your previous best. Using this type of training can enable a higher training frequency if the volume of exercises and total sets are kept in check, progress is much easier ( instead of having 3x5 to beat a certain load/# you now have one extended set via rest pause/ myo-reps, which can be manipulated either by more load or more reps, and a single set using these principles can be enough to stimulate great strength and hypertrophy increases.)
I use rest pause sets and workouts very similar to what you are using now on your upper body days and some of my best progress has been made using these methods, even though I have been training for several years. For example, say you have a previous best on military press of 185x7, 5, and 3, for a total of 15 rest paused reps. The next time you perform that exercise with 185, you end up with still 15-16 rest paused reps, you can easily take a short myo-rep style pause, and perform one or two more reps to break the previous pr. Many times this will be enough to push you over that hump and the next time that particular exercise comes around in your training, you are able to break your previous 3 rest pause set record in 3 rest paused sets, convincingly. There are about 1000 different ways to incorporate it into your training but those are just a few examples.