Another person that's tried merino wool underpants and is not a fan.
Biggest problems i had are
1/ Merino wool doesn't wick very well, so once you start sweating rather than that moisture spreading over a larger surface area it stay localised.
This means it takes ages to dry and you end up very very sweaty in the areas you really don't want to be sweaty.
2/ Other problem i experienced is that the fabric loses it's stretch after a day or 2, so you start with nice stretchy pants that hold everything in place, but end up with lose baggy fabric that doesn't hold anything.
3/ Takes ages to dry
I have Merino wool tops and they're great in certain conditions, but IMO using wool for underpants is the wrong material for that area.
I personally wouldn't buy wool underpants again and i wouldn't recommend them, if you are approaching this from a different angle than say Icebreaker or Smartwool, with a better solution and mix of materials then i would be willing to try them.
So if need any hot weather testing i am in Greece.