I quickly went through 2 Ozito headguns with both of them failing after only a few roasts. I returned under warranty both of them to Bunnings and ended up with a Ryobi variable and 200+ roasts later couldnt be happier.
I would return it and upgrade. As for the sparks? sometimes I get some chaff or general dust igniting as it blows back towards the headgun and this can appear as very small sparks which disappear very quickly.
But the Ozito is what it is...a cheap heatgun and will have a very limited life in the sort of use needed for successful Coretto roasting.