I wouldn't worry too much. They are a LCC, so don't expect anything fancy and you won't be disappointed.
I always bring a small bag onboard that fits under the chair in front of me, but I noticed several times that prior to boarding the ground crew hands out labels for the bigger trolleys so that they are allowed in the cabin, without checking if these people actually paid for that privilege. Since they allow 70 trolleys max in the cabin, I wonder what would happen when a paying customer doesn't get that label, because they reached the max.