Like you, I had cause for pause when I considered Vueling. There are complaints about just about every airline these days, so we pressed forward.
We were actually quite surprised with how very hassle-free our check-in and journey was from Barcelona to Granada, Spain. Our checked bags arrived safely on time.
It is advised to purchased the rate category that includes luggage (and then watch weight/dimension limits for carry-on). We normally only travel with carry on, so we checked our RS rollaboards, and I had carefully packed totebags (for the Vueling reduced carry-on restrictions). Before I checked our luggage, I asked the airline rep if she needed to weigh our carry-ons.....she took one look at them and said 'no problem.'
When we loaded the gate bus with the other passengers to be taken to the plane, I was surprised at just how large some passengers' carry-on was, and some had two bags each (with no problems encountered). But, you know how that goes, rules could be enforced at any time.
Vueling is evidently part of Iberia. I looked at fare quotes thru both brands, and even though it would have been the exact same plane for each, Vueling's fare was less expensive. (But, who knows, Iberia's restrictions may not have been as strict....I didn't compare.) I booked way in advance and the fare was so low, it was amazing.
Seats were not large, but definitely okay for a shot-hop flight. We are tall.
I'd book w/ them again.