How good-tasting are we talking here? I see references of no poncirin resin, but is there even a hint of poncirin in the flavour profile at all?
I've got some Monticello citrumelo, and I was hopeful this would be as close to pincirin-free as possible...but the hunt continues. So far I've yet to see fruit on my pragues or citrangequats, the shield orange is trying to call it quits, and my Yuzus didn't make it thanks to a particularly evil muskrat.
Monticello is almost free of the piney Poncirus flavors but as you mention it's still not perfect. It is better in flavor than aroma which seems to have more of these components.
I find that Iva Swingle is also close, and I consider it better than Monticello. It is edible down to the pith with no bitterness, but a sensitive palate will still detect some Poncirus flavor.
I'm not sure we can really get rid of it in a 50% hybrid, but it makes me curious about a Citrumelo back-cross involving pummelo or grapefruit.
Yuzu, Prague, and Thomasville/Augusta Citrangequat should all be free of such off-flavors, so you may enjoy these fruit more.

