I did hard VO2 max hill repeats yesterday. Tough workout, but I could really feel the benefits. I’ve been doing a lot of hill training in general this year. I found that my climbing ability was a glaring weakness in my triathlons last year. So I’ve been addressing the issue. I think I’ve made a lot of gains since January.
So I recommend the hill workouts too, as long as people ease into them gradually. It’s important to give your legs, especially your knees, time to adapt to the new stress.