I would like to get the Zwift Hub but I am not sure which cassette should I get. Currently I use my gravel bike with a Shimano GRX 2 x 11 speed, i.e. I would need to order the Zwift Hub with the 11-speed cassette.
However, in three months I will get a new bike with 2 x 12 Shimano Ultegra Di2, which means I would need the 12 speed cassette.
What would you do? Order with 12 speed and get a cheap 11 Shimano 11-speed cassette fpr the next three months or order with 11 speed cassette and get a 12 speed cassette later (but which one?).
The Zwift provided SunRace cassette is a cheap one and you’ll probably get better results with a Shimano cassette. In your situation I would order the Hub with the 11 speed cassette and buy a real Shimano 12 speed cassette to use with the new bike. It doesn’t have to be an Ultegra cassette - 105 (R7100) would be fine if you are happy with the available gearing on it. I would pick a cassette with the same gearing as you have on the rear wheel.
You will need a Hyperglide lockring tool and a chain whip to swap out the cassette, or take it to a bike shop. Using a torque wrench is recommended for installation but not required. A 12" adjustable wrench will also work. Depending on how tight the lockring is, it can require a lot of force to remove it.