Just wanted to post about this and share my experiences - I bought the Simply Light Designs Trail Winder underquilt with the modular insulation back in October of 2021 for use with my Dutchware Chameleon hammock. Since then I've gotten almost a dozen hangs in with it. I purchased mine with 3.6oz of Climashield and the additional insulation was also 3.6oz Climashield. This combination would cover 99.5% of what I camp in (20*F - 85*F).

Having the ability to add or remove a small insulation piece from my underquilt is a fantastic idea in my opinion. Now I have one underquilt that I can use all year (for me anyway). Warm weather? No problem, just use the underquilt with the built-in 3.6oz insulation. Super warm weather? Just leave the UQ at home or in the bag. Going to be colder? Simply snap in the additional insulation pad and you're good to go.
I'll caveat this with the fact that I do not camp in anything REALLY cold.
The majority of my hangs using this underquilt have been in 50*F - 75*F weather. Using just the underquilt without the extra insulation suited me fine in these temps. I have 3 trips in where the weather was in the low 30's and upper 20's where I used the additional insulation. It kept me nice and warm all night.

Setup is easy - it's two carabiners which clip to the ends of the gathered end hammock, and an adjustable shock cord in the middle side to cinch it up to your hammock. A total of 15min of adjustment, with the majority of that explaining to my wife where to tighten the underquilt as I was laying in it. Done and good to go!

All in all, I do not have anything bad to say about this underquilt which were not self-inflicted. If I had to do it over again, I would have chosen a different color - mine matches my hammock, so it's hard to tell the different layers apart when they're set up. The only other wish-list would be for a few more choices in the modular insulation - I'd have liked to have a 5oz option for the modular insulation.

If you're thinking of getting this underquilt I would highly recommend it. If you have any questions about my experience, let me know!