I do not think this is an appropriate tool for the level that you and your horse are at right now. I don't like them for 99% of horses anyway (won't say there is absolutely no place for them, but instances where they are appropriate are rare), but certainly not for a horse who has yet to achieve forwardness. They are difficult to get adjusted correctly, particularly if you do not have a very experienced person to guide you, and an incorrectly adjusted Pessoa will create a whole host of problems. I also do not believe that this is a good tool for *teaching* a horse to use its back - to the extent the Pessoa has an appropriate use, it is strengthening the back of a more trained horse who already knows what is being asked of him.
I do not mean any disrespect, but your side reins video a while back showed that you are not yet ready to use side reins correctly in your lunging program, and the Pessoa is 1000x more complicated (and more disastrous if used incorrectly) than side reins. Focus on your riding and enjoy your horse; save tools like this for well on down the road, if ever.