Hanging-off definitely works because you can keep the bike more upright using your body as a counter-weight, but going as far as a knee down seems a little "fabricated" on a bike like the TDM? Mind you, at my age I am glad to get my knee over the seat

I am slowly getting to that age as well

On the XTZ I get on the left foot peg first before I throw my right leg over
As implied in the last remark of my previous post the KD on a TDM indeed has more bar-talk than real speed gaining benefits. But still, the amount of hanging off I needed to do on the TDM to keep it upright enough as to clear the center stand / foot peg was already that involved that there was not really that much effort into putting the knee down. But it does take extra effort so indeed, in hard numbers it will slow you down.
(although it does still help you get a feel for the amount of lean angle you have an thus how much ground clearance is left)