I managed to make 5 gallons of Quince Cider 2 years ago.
As everybody has stated the fruit are very hard and pulping them to extract any juice is time consuming
After burning out SWMBO's fruit juicer I too resorted to the food processor and, eventually got 5 gallos of juice - very sharp and very low SG, 1034 rings a bell.
Anyway got it fermenting with cider yeast, dropped into a corni to get it off of the lees, left to condition and bottled it all up.
Took the lot round to the mate who gave me the quince, to a function he had organised, with a Portugese theme, evidently Quince Jam is very popular over there.
Everyone was handed a bottle and glass to try the "cider" and the verdict was
:sick:
Definitely not worth all that effort, so never again for me