In principle, this bag can be taken on board as hand luggage in this size. I have not had a problem with it on any of the 9 flights I have taken so far (4 airlines). BUT: As usual when flying, it is worth checking the hand luggage regulations of the airline in question before booking. The conditions can differ or change depending on the airline, the area where you are flying and over time.

The basic dimensions correspond exactly to the Star Alliance hand luggage dimensions. I also had it with me on the plane. The bag is elasticated, i.e. it can "inflate" depending on the contents of the pack and can then possibly be objected to. Which could be annoying.

Easyjet has the dimensions 55x40x 25, which is exactly the cabin size of this suitcase. You must not fill the suitcase to the brim, otherwise it will be 30 cm and no longer 25 cm.