I have a couple of them and they're useful for all sorts of things from sawing logs and making shelves to holding large steel bars while I hacksaw through them and subbing as an engine test stand for (as with Neil) FAI-F3D pylon racing engines. In fact back in the days when I competed in FAI-F3D my team-mate and I used to take two workmates to every race meeting - even the European and Wold Champs ones (my F3D workmate has tens of thousands of air moles!).
At race meetings they could be used to hold the engine test stand, and then with the jaws about 4" apart and a folder towel thrown over the top they formed a perfect model stand for working on models between races. The fuselage sat inverted in the gap with the wings lying on the flats in a perfect position to remove the cowl, motor & pipe, clean it all down and then refit & tape-up ready for the next race. If there was a wind it just needed a bungee strap lightly over the top to hold it all there safely while I went off to call for my team-mate. Then with a square foot of 5mm alloy plate clamped in the jaws they made a perfect field-hearth for re-brazing pipe brackets onto pipes and repairing undercarriages with technoweld.
I have one of the early die-cast alloy ones and one of the later pressed-steel ones. There's nothing much to choose between them - the little plastic clips that keep the feet stowed when it's folded up have failed on both, but that's just a minor annoyance. If pressed I would probably prefer the steel one because I can stick things to the sides with magnets, and because if it broke the pressed steel parts can be easily repaired with some steel sheet and pop-rivets or silver solder. I think the alloy one would be tricky to repair if any of the die-cast bits broke, but neither shows any signs of breaking so it's a theoretical concern only.
So I guess that's a big positive recommendation from me!
AS