I've bought the membership for GT as I find the app is more like having a real instructor with you. I think it will serve me better in the long run as I grow as a guitarist.
I did try Yousician and am still in the 7 day trial period. I like that app too as it's fun and easy to play and practice using their unique bouncing ball trainer.
Would it be a waste of money to pay for both? Like I mentioned, I'm definitely sticking with GT as my primary trainer. My goal is to learn the electric guitar (I have a Fender Stratocaster). Interested in hearing from others.