Cautionary Tale: when the airline baggage rules are different for the return flight!
I and two family members flew from Bordeaux to Valletta with Volotea. We all had "cabin-sized" bags but the conditions said we could put them in the hold free of charge or pay for "Priority Boarding" to carry them in the cabin.
Fearing the loss or delay of all our luggage, but not wanting to pay for it all to go in the cabin we upgraded one flyer and put a change of clothes for everyone in his bag.
No problems going out: we and the bags arrived safely and we had a great holiday.... buying a few souvenirs including a bottle of the local speciality drink, Kinnie. No worries about getting it through security after all, we had two bags going in the hold..... which we packed accordingly.

However, when we checked in for our return it was purely by chance and when the bag with the Kinnie in was (fortunately) already on the conveyor to the hold (pure chance... it could easily have been one of the "wrong" bags) that we discovered that the baggage conditions were the other way round going back to France!
Only the traveller with the Priority Boarding got to send his bag to the hold.... the rest of us either had to pay extra to put the bags in the hold, or carry our luggage through security and cram it into the overhead lockers.... which led to scenes of absolute chaos on the plane as there were far too many cases to fit into the available space.... which hadn't been a problem going out because it was all in the hold.

If lowcost airlines want to operate like this, then it's their call, but I really think that they should mention it clearly so we can make our choices accordingly.

Anyone would think it was a money-making ploy to trap unwary travellers and force them to pay extra fees.... surely not............?