I own both 150 and 200 weight IB briefs and t-shirts. I use them daily at work, 12+ hours at a time for the past two years (EMS). Everything said about merino wool comfort, wicking, and b.o. control properties is true. I love it!
The briefs fit next to skin, but not tight. The legs are shorter than most boxers I've owned.
My biggest knock is durability of the lighter fabric (150 weight). I've pulled off both the lightweight briefs and t-shirts and had my fingers go through the fabric, requiring repair (stitched them up and still in use).
Also, the brief's waist band rolls or folds up on you. I prefer Smartwool's band that is wrapped in fabric.