I REALLY hope I don't ruffle any feathers here, since I respect and like everyone here.
I was trained by the instructor that has issues with the Fusion, (a guy in my class had one), and when objectively laid out, (which they were), I agree with the issues. (And I'm hoping I don't offend you here, Lynne, you're one of my most respected posters.) The issues are not "brand-specific", but "specification-specific". I won't go into it here, but it was compelling and I agreed with it.
Owning-up, up front: I dive a DUI, but mostly because my local shop was a DUI dealer (only DUI), and I had just done a DOG Days and was digging on DUI. I bought one, it worked out. I own a TLS-350, (apparently the most hated and evil drysuit in existence and one that is allegedly made entirely of leaks and cold.)
That said, mine's been watertight from day one, and I stay warm with the proper insulation. Please don't think this is a "DUI v. Fusion" deal. Our instructor put my DUI next to the Fusion and went point-by-point why the DUI, (or another trilaminate-style suit) was preferred by him. It made sense and was extremely well-thought out and borne out by his experience. I deferred to his experience and knowledge.
That said, as much as he allegedly "loathes" the suits, he never gave the guy diving one in our class a hard time or made an issue of it. If anything, the guy diving it gave himself a hard time by under-inflating it. He constantly dove with a constant "20-foot squeeze" to, in his own words, "make life easier on myself." He had major issues in class, to include going hypothermic on the last OW dive and requiring minor aid. (Though that was HIS fault, not the suit's fault.)
I hope this is message is OK. Thank you.