I have a shield9 and was thinking about this system.
Due to my country's regulations I have a limited amount of guns, so this is my ccw and range gun for now (planning on getting a revolver later), so I want to be as good and smooth and awesome as possible, I dont mind the recoil of the 9mm but if It can be better, well... I like it!

So, my question is, do they really work? Because I dont want to spend $77 if its not going to improve haha

Unless your having issues with factory rsa all your doing is wasting your money! Especially $77 for a rsa.

I can only comment on my experience. I picked up this system to try in a M&P45. All my M&P45s are exceptionally accurate and downright boring at 25 yards using my standard 185JHP reloads cranked out of Dillon 550B. I watched the group size double after installing the DPM system. Dropped the stock RSA back in and the groups went back to normal.

I'm not saying the DPM system is flawed, but more so saying it's common knowledge certain loads can be fine tuned depending on spring weight. For me, it was an experiment that didn't work.

Don't do it!!! Snake Oil!!! Those things are a waste of money.

A few top-notch professional shooters have used these type of systems in their competition guns, along with other mods. That said, I'd argue that if they were really effective or helpful, you would expect to see them widely used in competition or among shooters generally. You don't. It's mostly folks new to semi-autos that find them attractive and most of those units end up retired pretty quickly.

There may be a better way to spend your money.

Buying more ammo can let you practice more, but the problem with more practice is that you must be practicing the right things using the right technique -- otherwise you're just developing or reinforcing bad habits!!

A group from our IDPA club, some years back, had an instructor and his assistant come in to spend several hours with us one evening and it was a great experience. You'd be surprised how a modest amount of training (at a moderate cost -- maybe $100-$150 per session) can greatly improve your effectiveness and comfort when using your weapon. Local IDPA or USPSA clubs should be able to help you find a well-regarded instructor if you feel the need.