Please give it a go. Sorry if this sounds like self promotion, But I have just sold a T.M on the basis of this recipe alone.
As noted above, sometimes it is difficult to know how "set" a marmalade or jam is prior to ending the cooking cycle.I keep a stainless steel pinch bowl (small saucer) on top of a saucer of crushed ice next to where I am cooking and to test just drop a spoonful onto the dish and immediately invert it. If the material doesn't run or drip, the jam or marmalade is done!If I want a "looser" or runny product, I watch for it to track slowly across the dish. If it runs too rapidly and drips off the edge, I know it requires a bit more cooking time. I've been using this method for years and find it works better and takes less time than anything else.