How does it work in practice? If you are massively irradiated, does your HP heal very quickly?

Was it worth it to put 70 points into your Survival in order to unlock Rad Child?

Rad Child grants 2/4/6/8 health per second (or...per something, the GECK is somewhat unclear here) at 200/400/600/800 radiation (the different poisoning levels).

Certainly sounds worth considering while on hardcoe mode. Although being able to heal without consumables or visiting a doctor is kind of going against the whole intent of hardcoe mode.