I believe the additive helps restore or prolong the life of the fluid and would enable you go shudder free for long enough to trade the car in and may last for a year, but it does not seem to be a permanent fix on it's own. Poor fluid plus additive might become OK fluid for a while, terrible fluid plus additive would only improve to become poor fluid; good fluid is the only real solution.
Your method of flush, change + additive sounds like the ideal method and should have lasted longer than 1500 miles, hopefully this is a blip that will resolve itself. There are others on here that can chip in with start clutch reset/learn procedures which may also help.
I added the manual version of the Xado paste when I changed the gearbox oil, but I don't know if the new oil or the Xado made my 1st gear change slick again or for how long.
For other readers & google searchers:
Shuddering Honda CVT gearboxes really need a transmission fluid flush & change using Honda CVT-F. Honda now recommend the fluid is changed every two years, although that will vary with driving style and mileage. Older secondhand CVT cars are quite likely to have old fluid.
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TG
