I don't know how the experience levels range in your group. I think for most beginners Nashville numbering is going to cause more confusion than help. (And, BTW, I
love Nashville numbering and use a modified version of it all the time when I'm playing bass.)
I think it's good to present the theory to help them understand song structure, but most beginners probably aren't going to be able to translate "1 = C" "4 = F" and so on in real time any better than they could, say, transpose "G = C" "C = F".
In essence what you're forcing them to do is transpose everything they play every time - I think that's tougher than just the occasional transposition of a single song.
Now, if you're playing with more experienced folks who use a lot of barre chords and understand how you can "box" the song using them, Nashville numbering might be appropriate especially if you do change keys frequently. This is why I use NN on bass, the band leader can change keys all he wants to accomodate the vocalists and all I have to do is move the box a fret or two.
If you're interested, I've prepared a one-page chart that shows two different "boxes" - knowing Nashville numbering and these two boxes allows someone to play rhythm to just about any song in any key even if they've never played it before. You're welcome to print and distribute
this chart
Just my $0.02.
John