in my experience + that of friends, neither the pub prop nor the d'angle are foolproof; & in addition both re quite pricey for what they are.

i've made guitar/ banjo table clamps that are as practical as these pricey ones but only cost about 50p.

anyone can make one simply- you need a small woodworkers 'G'clamp- about 50p from the market + the plastic handle from a 5 litre lemonade bottle.drink the pop, then if you're chucking the empty bottle away, then the handle's free. cut the handle off the bottle.

just cut the handle midway & clamp it to a table, using the woodwork clamp.

because plastic handles of this shape have a gene memory of how they should be shaped, when you stick your guitar/ banjo/ other thing into it, it'll remember to come back together & will hold your thing securely

cheers

mr h