I really enjoyed making this, and the end product is acceptable - good, even - but a bit too bitter and a bit too hard.
I used a large grapefruit instead of a small one, thinking that would be okay since my limes and lemons were small, but I would advise against this. I'm pretty sure it's the grapefruit that has made the marmalade too bitter.
Also, my marmalade reached the gel stage at 25 minutes, or maybe even earlier. I wasn't even ready to check it yet at 25 minutes, since the recipe says it should take an hour, but I noticed the mixture starting to gel on the plate where i was laying the mixing spoon, so I stopped the boiling early. I haven't opened any of the jars yet, but the bit of leftover marmalade that went in the fridge is almost as hard as a gummy candy. I'm new to jam-making, so I'm not sure why this is, but I would guess I overcooked it. Maybe I should blame this on the grapefruit, too, but I wonder if the hour-long boiling time in the recipe is a mistake, though. Even forgetting the time required to cut up the fruit, wash the jars, and bring everything up to boiling, the times listed at the top of the recipe and the times listed in the recipe don't match up. The recipe itself asks for 45 minutes of boiling the fruit, 1 hour of boiling the marmalade, 10 minutes of water bath processing, and 5 minutes of cooling, but the top of the recipe only says 10 minutes of processing and 1 hour of prep.
One more thing: I would have appreciated more detailed instructions on how to cut up the fruit. I cut it up just fine for my liking, but "paper thin" doesn't seem possible without decades of practice or some type of machine.