I suppose there are different kinds of gel rests. Many, many years back we had a mouse pad with integrated wrist rest. It sucked balls, not least of which was because it was constantly in the way of using the mouse, but it also felt too spongy and dirty. The rest in the first picture (second broken and needs to be opened in new tab...) I use with my trackball. It's a fairly solid gel and really comfortable. I do have the Griffitis for my Ergodox, but in comparison prefer the gel one, the gel rest not only eliminates the two pressure points at the base of the hand, but also allows for better mobility while resting your hand (convenient for gaming or short-cutting) and there's less sweat (the Griffiti just feels really sticky after a while). It's only around 6-10€ as well.
A completely different idea is to get something like the Ergorest. I've been meaning to get those to give them a try, but they are a little more expensive to just "try out".