My clutch went, but I was in cornwall at the time I had to drive hundreds of miles back to London, by which point it was slipping like crazy. Sometimes you get lucky, the flywheel is ok, but if you don't order it and you spend hours opening the transmission up and find the flywheel is damaged then you have wasted a lot of time and money as you will have to order another one and do it another day. Most dealers will (hope I am not dropping anyone in it here!) allow you to return an unopened flywheel if you dont fit it...so order both, if you need it fit it, if not send it back unopened.
As an aside, if the clutch is slipping, it usually is already too late to save the flywheel ...
... and yeah, lots of younger drivers picking up Zeds, maybe more powerful cars are becoming relatively cheaper. At 21 I was in a 1.1L Fiesta with insurance of £850, more than I pay now on my Zed, that was 16 years ago!