of course it will be painful -they take a hammer and chisel to a joint :)
However, it's a different kind of pain to the wearing, getting you down everyday type of pain you get with knee problems and as a bonus, it recovers quickly. Recovery time is all subjective, especially to how bad your problems were before. Six weeks to feel much more normal and to feel it's actually your leg you've got on, three months to be "getting there" six months to be completely normal and over it, 1 year to completely forget you ever had a knee problem.