WV Hiker, let me brace up my "flimsy" soapbox.
You are correct I have never personally used an Icebox to make an igloo. Like Bob, I have handled them; I was looking to purchase one myself. I have read and re-read their literature and viewed the videos they have posted, as well as many others posted on Youtube. I have build an igloo right next to one being used (they took longer to build theirs than mine). I think I have a good understanding of how they work and if one was handed to me I could probably use it without instructions. So I would hope I am able to make a educated comparison.
You wrote "It seems to me as though many in the UL camp become extremely frustrated when someone even so much as suggests using something that is a bit heavier"
That sounds like most of the people in main stream backpacking circles.
I don't need to go out and use a 7 lb ArcTeryx backpack to know that it is too heavy for the hiking I do, no matter how well built it is or how bombproof it is. Yes the ArcTeryx pack works for backpacking, but there are other options, that are better suited to the objective at hand. My old 4 lb Gore-Tex hiking boots work, but my 1 lb trail runners are better. My old 10 lb tent works, but my 1 lb tarp is easier to carry. My pots, stove, clothing, etc, etc, etc... I hope we (those on BPL) are trying to find the best system, which admittedly is not always the lightest option.
Though not very romantic, for this application (igloo building) a lightweight shovel, snow saw/knife are all the necessary tools needed to accomplish the desired objective.
In backpacking there are some great "tools" out there, but in the lightweight arena I feel my method is the better way to go. YMMV
edited to add: Sorry for pushing back so hard- to me its like someone saying "its simpler to use Leatherboots for hiking". I would probably get a little unnerved with that comment also.