Isotonic powders are generally better, even in a weak mix is what you do. I've used gels in a sportive when I'm low and have been on for setting a time. If it's general training, don't use them. Mix of malt loaf, fig biscuits, isotonic powders, bananas are enough. The odd gel is enough for a fail safe.
That said I did do a 72 mile commute last week, on a couple of wheatabix, 1/2 strength orange, then a few sarnies at lunch and a ride back with just water. The ride back with just water was not enough as I'd not had time to recove properly