I started using gunner training this semester (M1) and I like it. I do well with conceptual classes (like phys, if you understand it, there isn't much to memorize) but I struggle with straight up memorization. Gunner training seems to be helping.
It got a little overwhelming at one point, because I banked too many flashcards at once and then took a while to get to the mastery level so I was having 100-120 questions a day, which is a lot with classes. Now, I'm more careful about that and get around 60 questions a day, which is manageable. I usually do them before class or right before bed, depending on what time the day's classes start.
Gunner Training is great for straight up memorizing. It's not intended (in my opinion) for use as a primary learning tool.