I have the hold-n-treat as well and use the key, but once had to explain what a type 1 MSD was and that it was impossible for me to discharge unlawfully, even though the unit has big stickers right on it. My valve is always "open", but I have a key with lock for the controls. I've thought about putting the valve handle on "backwards" and securing it with a lock, just to not have to answer stupid questions.
I got the idea from the 20g propane tanks. Remember when the industry decided to not fill all the old style tanks? I had 3 tanks that were produced with the "new" valves, but with the old round handles instead of the triangle ones that the new valves standardized on. Even after pointing out that I had the new safety valve, the fill people still would not touch my tanks. So I simply went home, started up my foundry, rammed up a mold for the new style handle and poured myself a batch of new style handles in aluminum. Suddenly, my bad tanks were good again. (I had a lot of requests for a continued production run of new style handles, but decided not to for obvious reasons, most of those who wanted them did not have the new style valve).
Anyhow….I get tired of having to explain things I don't think I should have to. It's just how my mind works. After all, its optional for me to understand that level of detail, but should not be optional for someone for who it is their profession. It grates on me more than it should.