Hi to Everone
I’m new here but old flashlight user.
Few torches from few producers bought “for use”.
Recently I bought some Convoy’s “for DIY” (plus parts)
S16 o M21B will be more compatible with S21B structure ?
Tail’s, modified switches, threads, maybe driver
Urban legend says, some problems apply for me with M21B ?
I’m not hunter, soldier, rescuer - no specific / high expectations about “beginners thrower” torch, S16, M21B will be (alone) OK.
It’s good to have you here, cosinus!
Thanks, nice day
maybe I should wish “dark night to You” 
I have M21B, S21B and S21D. M21b is slightly larger, so the head can go on S21B body but not vice versa. S21B and S21D tubes are compatible.
So I would recommend S16, not M21B, for the purpose of compatibility with S21B. S16 looks very similar to my S21D and hopefully shares threads.
Purchase via internet, a dose of uncertainty.
Yes, S16 is compatible with S21B, tubes and tail switches can be mixed.
S16 with SST40 and smooth reflector (maybe SFT40 in future) is kind of “pocket thrower” that fit good to my requirements. I glad.
Small ring of light from stainless steel bevel (which I checked) is not important for me…
I think it’s more of less a tie. Same drivers and switches between all 3. The threads might be different with the m21b and might be the same with the s16 but idk, they get changed up now and then.