I got a bunch of SIS gels and “Go Hydro” drink tablets last year through various promotions - it all tastes pretty awful and consitently gives me stomach issues. The Gels are definitly more convenient on the run than Gu, since they are pretty watery.
I’ve used Skratch for years now (Pineapple, Passion Fruit, Matcha), IMO Skratch tastes way better, more subtle and natural tasting. I’ve also never had any stomach issues with Skratch, even when I make it pretty dense (4-scoops in 24oz).