I have the Fusion Tech (soon to be replaced with a Santi), and I've been pretty happy with my Fourth Element underwear. I wear a base layer, the Xerotherm, and the two-piece Arctic for Northeast diving, whereas the base layer and the Arctic are just fine for the Floridian caves. I was not terribly impressed with the Whites MK2 undergarment that came with my drysuit. That's partly because I am pretty short, and the damn thing was miles too long for me, so I had a lot of excess material bunched around my waist. The jacket was also a "straight up and down" affair, and did not follow the contours of my body - I have an hourglass shape, so I either had to yank it down over my hips, or pull it up so it ended at my waist - where I already had a lot of excess material from my onesie undergarment. If you're not a short woman, this is probably not relevant to you, but it was a huge PITA for me. I have had lots of drysuit floods, and the Arctic kept me fairly warm and dry - the MK2, much less so.