There's nothing wrong with flydubai for a short flight, especially if you are terminating in DXB, as Terminal 2 is not a fun place to originate, and I would also advise against using flydubai for connecting itineraries.

Their aircraft are new and clean. I cannot speak to your question about whether they are more cancellation-prone than other airlines, but it's not a bad choice for your circumstances. The main down-side is that there may be long lines at KWI, as this airline doesn't have on-line check-in (except for a few routes), which seems bizarre for a start-up budget airline.