Carry on baggage size - Ryanair; anyone tried one of these?

[Dog Star]

GF is off with her mates for a classy weekend in Puertobanus (or whatever it's called).
She's got herself one of these
http://www.matalan.co.uk/homeware/travel-essential...
Which conforms to what Ryanair class as carry-on size, but I'm a bit worried as the 20cm measurement is where the wheels are and it might not fit in their thing for testing luggage size.

Are the "forms" they test luggage in absolutely the same size as the stated dimensions, or is there half a centimetre each side etc?

[silver_lining]

My parents flew last week with Ryanair with two of these without any issues.

[popegregory]

If the wheels are an issue, turn it upside down before putting it in?

[Dog Star]

silver_lining said:

My parents flew last week with Ryanair with two of these without any issues.

I love PH! Ta!