It's great. A bit hard to stomach at first, as you're cramming 100 calories of something with the consistency of peanut butter into your mouth.

They're absolutely wonderful for long-distance running. Every 45-60 minutes (typically before a water stop), grab one out of your pocket/belt, bite the head off, squeeze the gel into your mouth, put the discarded head and packet in your pocket (or toss it on the ground if it's a race and littering is expected), and keep running.

They should be available almost anywhere running stuff is sold.