Proline and glycine supplementation- benefits and side effects?

I bought proline and glycine powders, separately, because as main AAs of collagen, they could help muscular/ tendon recovery post surgery.

But slightly concerned because I see some research on proline metabolism and cancer.

In any case, would like to hear from folks who tried proline and/or glycine supplementation on how long they've used them for, what benefits they've seen, and what side effects personally experienced, if any!