I have tried the most popular MX switches. My buddy has a switch tester, granted it's not a great representation since you just click one key repeatedly and it's not a full experience. I have also tried a full keyboard of Romer G switches on a Logitech board another friend of mine has. I couldn't say for sure what kind they might be if there are different versions of Romer switches.
That's one of the GMMK's benefits, you could pop any switch in that tester, or from a loose pile, into the keyboard and play with it for a while in an actual board. The only Romer Gs I have tried are linear. I'm not particularly interested in linear switches either way, but I am not a fan.
The switches are made by Omron, of mouse switch fame.
He also has a Model M and I believe those are buckling spring but I cannot imagine those are popular today, not in "modern" keyboards at least.
Unicomp
still makes membrane buckling spring boards, direct descendants from IBM's tooling. They have their fans, especially out of principle and respect for a company that keeps the switch type alive.
Ellipse is all but finished with
realizing a rebirth of the IBM 4704 family of Model F keyboards, with capacitive buckling spring switches.
Fans of clicky switches are highly likely to like buckling spring in one form or another. The board in my profile picture is one of Ellipse's new F77s.
I've been very happy with clears the past several years and don't really have any complaints about them. I like the actuating force they require and the tactile feedback is nice. Browns are a step down in the actuation force and I don't particularly want to take that step down but it's looking like my options are slim. I will take a look at the GMMK you recommended and see if I can configure it in a way I will like.
MX brown was just one example, tactile fans typically usually go for one of any number of boutique MX clones,
like from Zeal. Being a clicky guy, I like my tactility sharp, and having not bothered to try boutique MX clones, I like Alps or Matias tactiles if I had to use switches of that type.
If your only requirements are MX clear and RGB, then the GMMK will work. If you have any other parameters, we can try to find something else that fits.