I'm fairly certain cables longer than 50cm are included in tablets. You'll be fine, you might even have space to route your cable behind your desk and into the back of your pc.
I bought a Wacom CTL480 and it came with a really short micro usb cord. I tried buying a longer micro usb one but it didn't fit in the port because of the rubber cable connector part...
The cable length for the Huion 420 is 1.5m from what I read.