I've to fly soon too and thought about this..
You save 30 euros or more by taking 10KG onto the plane, instead of putting 15KG into the hold, and you'd also get the 10KG in the cabin even if you use the hold I suppose, only thought of this now.. hope 10KG by itself is enough. It's only 5 days in the sun, woo hoo... so don't need much.
Anyway.... I wonder how they check the bag size?... the best way would be to have a box which folds out to the maximum size and is placed over the suspect bag, if it goes over it's ok. They might pass a cutout over the bag or just measure it with a tape...
You'd want to make sure your bag doesn't sag over the limits
took me ages to book, website kept saying 'timeout'.. even on two browsers and after i deleted some cookies as well...