@jud I suppose if you do them, it might help to increase your flex, even though you may never be able to get it far back like people do who have never TKRs. I think moving the seat forward on a recumbent bike so you have to flex more helps in that.
For me, the biggest advantage of increasing my flex would be to able to kneel more easily. When I try to kneel (on a cushion of course) I feel like I am going to topple forward because I can't bend my knee enough. When I spoke to my doctor about possibly getting the lysis which would hopefully increase my flex, I asked him what the advantage would be. He said if I lived in Japan I would need the flex! I am sure that is true, but it also prevents me from getting up and down from the floor easily so I am intimidated at the thought of trying to do yoga. I would not put myself in a great deal of pain to increase my flex, but that is my personal feeling. It all depends on what each individual wants to achieve.
JK