The comments that I made were based on the thread attachments at the end of Bettatail last comments, they are located at the bottom of my picture. He brings up some valid concerns about safety but they seem exaggerated.
After reading them I felt like I had a dangerous chemical that at any time could kill, which it could but not likely . It was almost funny because I had a CO2 DIY venting directly in my small study room for 3 months & never felt sick! I will not go back into it since I have already said my opinion which could also be wrong.
I think what has brought some confusion to me & maybe others is if they bought an older regulator without a solenoid it could be a little daunting to install which was not the case for me but I could see it being a problem for some. My solenoid came in the ( inline form ) if I stand corrected meaning hex nuts able to be attached at both ends ( not directly to the solenoid ). Until learning from you Anthony I did not even realize that the solenoid does belong attached to the regulator. Recently I started to look around to buy another regulator for a bigger tank & I noticed most regulators come now with built in solenoids. Seems like the way to go. The further downstream not attached to the solenoid works though, I know because I have been running it that way for years without a problem, but I can see a need for at least 2 check valves. In a matter of fact , I agree with what you said & feel most systems should have 2 check valves or more pending on what the configuration is.