I donate usually once a year.
Did it twice last year, but I think I'll stick with once a year.
I have a friend who donates blood (not on gear, just like to donate blood to the blood clinic) as often as he is allowed. I think he has been doing this 3-4 times a year for decades. He has no issues.
Personally I think as long as we are taking our fish oil and staying hydrated I bet we will not have issues with a bit higher hemocrit.
Donate once a year to make yourself feel better, lol.
I think donations would be better at removing toxic metals out of our blood. You know the toxic metals that might be in chinese powder gear, lol.