I flew them around Christmas from STN to Baden Baden. I was a bit concerned about the size of my carryon, a soft duffel bag shape, because I thought it was longer than the maximum length (unless scrunched) and asked them about it the day before my flight (when I arrived at the airport from another flight). They did not seem to care about the size, only the weight, and on both check-ins, it was in fact weighed but not measured. Because I'd bought my ticket relatively late (my plans had changed), I did not have a particularly cheap fare, but it was still the quickest way to get to Baden Baden from London. The flights were better than I'd expected (I snagged an exit row both times).
I may be going back this year and would do it again (but would try to buy my ticket earlier!)