You are not the only Marines, but having been released from active duty 43 years ago, I'm one of the older ones.
I took the basic SFG class last November, 10 months into KB training. The good news, I had learned my lessons fairly well from books and videos. The other good news, the training was excellent and helped me not only improve my TGUs and pressing, but may have prevented me from injuring myself. I have good hip mobility and can squat way down comfortably into relaxation. Too much tailbone tuck that I was not aware of and I'm now stopping a bit short of that when I squat. The goblet squats got me squatting with good posture and I'm doing double kettlebell front squats in the rack position and feeling good about my form, though I'm about due to video myself and look for the tailbone tuck again.
I recommend the class. It is single bell. I haven't done the cert, but I think it is oriented toward double bells and instructing.I'm just not ready physically for it yet. I'm only 64 so I have time to get ready for it before I'm too old, whatever that is ;0)
For the moment, I'm meeting my original goals and objectives. In about 14 months I've shed 70 pounds of fat and though I'm not yet strong, I'm stronger than when I started and feeling about 20 years younger (seriously). I've become a kettlebell missionary, former fat guy. I can let my bulldog tattoo show without feeling like I'm disgracing the Corps now.
So, the SFG class did me good and I'm glad that I took it. The cert? Maybe one day, but as I mentioned, at this time I'm on track toward my goals with what I'm doing.
Sempers.