Roller Bags
I think the problem is now, and may have been in the past, that they don't fit the "Gauge" at check-in. They also may exceed the weight limit, which seems to depend on the airline. I think that anything which encourages people to travel hand luggage only is a good idea. I don't know if Easy have changed their rules but they used to let you on board with anything up to 20Kg, so long as you could lift into the overhead locker yourself.