Go for it. I have one on the go all the time. As soon as one is finished I make up the next. Superb for those times when you open the fridge and think "what can I have?" The answer is JELLY.
You can make it wobbly or thick and globby. You can add cranberry juice, skimmed milk or yogurt, fruit, goji berries, all sorts.
I make one up with half a pint of boiling water. Defrost half a pack of frozen summer or forest fruits in a pyrex loaf shaped dish, pour over the cooling jelly and set. Then turn it out onto a pretty dish, decorate with some lovely soft fruits and maybe a few mint leaves, serve within a dish of low fat creme fraiche. No-one can believe it's "slimming food".
Looks divine and tastes great too.
Sometimes I have half a jelly, some fresh fruit chopped up, a WW yogurt or fat free natural yogurt and a sprinkling of cinnamon and pine nuts. Filling, tasty and good for you. Yum!