Well, from a purely physical standpoint, they do the exact same thing.......limit the downward travel of the arms to a desired point. How and where they do it is a obviously different.
I'm kinda partial using sections of fuel line underneath the pistons. Others might not do this or even warn against doing so as (especially in Mini shocks) it will alter the handling characteristics of the shock oil you are using, thus altering the handling.....even if only a tad bit. Viscosity from the tubing can create air bubbles, not allow the oil to pass freely or even tear.
I prefer the Fuel Line method as I run mostly minis anyway, I don't want to have to worry about piston holes lining up and it's cheap. I do have a few cars with the droop limiters and am not a big fan of them. The new Vendetta TC has them built into the upper/inner arms which, in my opinion, weakens those parts substantialy. I also feel that the tubing almost gives ya a little cushion if the arms/shocks get sprung whereas the droop limiters will just slam into whatever plastic or alloy part to which they are juxtaposed.