oh I agree that there are no real substitute for going to life drawing classes. But some of us just can't cause there are none at the times that we can go, literally none around within a distance we can travel, LOL or in my case, a leg in a cast for long period of time and now not being able to walk on it much until it fully heals which can be months
The key would be to really study things, drawing regularly from sources like these can still be super helpful XD