Good luck with your TKR. I had a partial knee replacement little over a year ago. So glad I had it done. Just work hard on the rehab and you'll be good as new.
As far as how long it lasts, I've had one friend say he needed two shots a year and another who said it wore off in a couple of weeks. I don't think you will get a concrete answer. It just depends on the person.
I ordered one about a month ago. Probably be another month until I receive it. I saw on Facebook they are taking more preorders for the Hellfire and Sidewinder.
Yes, you have to create an account. It doesn't cost anything. Somehow Pirateship is able to secure good rates. Most bats shipped weigh 2-3 pounds. Use the last address you did a deal with and compare the price on Pirateship versus UPS website.