Not in the knee but I did have on in the heel to help with a torn Plantar tendon/ Plantar Fasciitis etc.
I'm not gonna like it hurt like a Mofo, probably the most painful shot I've ever had. However, that may be in part to the location of the shot, being in my foot etc., but it was a day or two before I could walk on it.
Also, insurance did not cover it and out of pocket was $300+.
Not PRP but I had an amniotic tissue matrix stem cell injection for Achilles tendonitis. This was done in conjunction with electric impulse treatments.
It was a little tender during the injection, especially when the Dr hit on the sore areas, but nothing any worse than I've done to myself over the years during my "active recovery" periods and self-treatments. The soreness increased during the first 24 hours afterward but I was able to drive home just fine.