I tore a tendon in my ankle a few months before getting my bocks. It's still not fully headed up, probbaly never will but anyhoo, I couldn't walk for 2 weeks, took about 3 months for me to be able to run (and not for long or without being wonky lol) but..I was bocking a few months in. Never caused me a problem. your ankles and legs are relatively stable in the bocks. Since I had a kinda lack of movement in my ankle the right way and too much in the wrong way it was pretty good. For bocking at least both feet are as good as each other
Anyhoo, yes, its less, if you are worried dont go too high over. some springs are are not over stiff will be nice and soft, much less than running on floor. If you go well over to save money ect the difference will become less...but still better compared to concrete.
btw tho, running on these is hard, it wont be the answer to continuing to run. It is much more hard work, nothing like normal running ect. You'd be lucky to do more than a mile. Run on marshes!