Sorry to be late to the discussion. I was searching for official word from easyJet exactly on this subject - there isn't any - and hence found this thread.

My experience at Manchester is that when I have paid for an XL seat, I get fast track through security too. Every time.

For for usually very little extra (£10.99 on one of their longest routes, MAN-AYT), you get:

1) Priority check-in
2) Fast track security
3) Speedy boarding
4) Guaranteed larger bag (56 x 45 x 25 no weight limit) stays with you in the cabin (in addition to the second bag 45 x 36 x 20).

Not a bad deal IMHO!

Of course as FT without Plus or Flex is not official policy, this benefit could be withdrawn without notice. In the meantime, it is a blessing.

Tim.