Well, just to throw another wrench in, my favorite brand is Weatherbeeta - Lacey's had rubs with everything else (but, blankets and horses are like humans and clothes - one brand of jeans might fit great but the same size in a different brand might fit terribly).
I think pretty much all your questions have been answered and I don't know too much about those brands you're considering.
As far an experiences go, like Delfina's guy, Lacey has more blankets than she could ever literally "need" - 1 HW, 2 MW (one is pretty new, the other is a "back-up" that has seen better days), 2 LW, and one fleece sheet. However, I really like that she has that many blankets. I've kind of built my blanket "collection" over the years. The second year I had her, she only had that beat-up midweight (new at the time) which was fine but there were times that she got cold (even with a coat like a mammoth, but she seems to "run cold" as a general rule - except in the summer, she overheats easily too).
The next year (the year she came home) I got her the HW in the fall and we had a much better winter. Then in the spring, I splurged for the second MW and a LW - that was great because sometimes the first MW would get damp inside during one of those torrential PNW rainstorms and I could switch out a damp blanket for a fresh cozy one without increasing Lacey's warmth level.
The LW is perfect for the spring/early fall when it's just nippy enough to get Lacey cold but not literally COLD.
And then, I bought her the second MW last spring because it's a pattern I adore and....yeah, I have no excuse.
Actually, right now she's wearing her second (the old) MW. Her usual, newer, MW is nearly soaked through so I've given it the day+night off. The old MW is pretty waterproof but it is leaky (someone
walked under a low branch a couple of years ago and ripped it allll the way down the mid-line - I "fixed" it but you can only fix something so well, you know?).
Anyway, that is all to say that while one blanket can function in a pinch really well, sometimes it's relaxing to have options.
Oh! Also, out of Lacey's blankets, 3 out of 5 have shoulder gussets. 1 with gussets (the HW) rubs her something awful (I think it's a size too small - I was expecting it to be sized like a WB -WB's run big- even though it's a "Pessoa", silly me!) but none of the others rub at all, even without gussets. I don't know if that holds true for all brands/horse shapes but that's what I've found! :)