They work great; the only downside is added weight and (arguably) less cooling
The added weight means more pressure on your hands, more strain on your lower back and more weight on your sit bones / saddle. But if it works for you it works!
I've found lots of other ways to carry water that I prefer
Bladder in the frame bag, bottle cage adapter to put two bottles outside the frame bag, bottle holders outside the seat pack, feed bags on the stem, over the aerobars, etc...