Interesting discussion and couldn't help but chip in (I only ever eat homemade jams and generally only marmalades). Luannh, you might mean "Calamondin" it looks like a citrus (but I believe it is really another genus). Calamondins are terribly bitter (not like Cumquats at all even with the skin on). I am a keen fruit grower, mainly citrus and make marmalades out of all of them.
We have Calamondin, Clementine, Mandarin, Lemon, Lime, Nagami Cumquat (those are the beautiful oval ones) and a very old Valencia Orange. Valencia's may be a suitable substitute for Seville, they dont have quite as many pips but are very high in pectin and when overipe make beautiful (but tart) orange juice. I never add pectin to any of my fruits and so far have met with good success.
Love your Youtube vids Muv.....Mum and I have almost lost our "English voices"....Gosh if I went back to Devon they'd call me a foreigner
