I’ve seen a bouzouki player using such a clamp once at a session. You just have to screw it on the table, and it will hold a guitar or bouzouki, banjo,…I think they’re very handy to carry around, not as clumsy as a heavy metal guitar stand.
If anyone knows were they sell these, please let me know.
On second thoughts, these might do a better job http://www.musicroom.com/se/ID_No/0332240/details.html
Thanks a million Mike! I can’t go wrong with one of those !! This thing might even hold a pint glass 
Is that really such a good idea? If people bump into it, they might break the instrument rather that just push it a little.
Yeah, that looks like it would be a supplement, rather than a replacement for,
a floor stand. Doesn’t seem like it would hold the guitar up, just keep it from
falling over to the side…
I have a mini guitar stand much like the Hurcules stand you linked to. I love it.
It’s light and I can strap it to my guitar stand with velcro straps.
Those mini guitar stands are great for playing on stage, or in pubs that aren’t too crowded. The pub i play in is packed all the time and plenty people swaggering about. A stand can be easely knocked over, but this prop is more secure. Anyway, i wouldn’t risk playing an expensive guitar in this pub.