If you can make the trip without carrying ”a typical carry-on bag sized item” inside the cabin you are ok to go.
Their rules are atypical for an airline, and the size limit allows only small backbags in the cabin. There is no upgrade available either. If you have e.g. large backbag with expensive camera gear you want to travel with, you should probably use some other airline company.
When booking your flight, just pay some extra, both for the luggage, and for the seats. You’ll still end up with a cheap ”ok-ish” flight. Be ready to travel light. They will measure your bags multiple times (you can not escape that). Otherwise you might get really pissed-off at the airport for paying all the expensive extra fees.
About the actual flight I took: it was ok, short two hour light, modern plane, no food or drinks served, only water. I was more than happy with that, considering what I had paid for the flight.