Maybe your standard "hoodie" made of fleece or cotton is street wear but for the back country hoods probably provide the largest bang for your buck/oz when it comes to warmth. Your body loses a disproportionate amount of heat through your neck and head than the rest of your body, so covering that small amount of surface area with insulation (and keeping out drafts) will keep you much warmer than if you added that extra weight to torso insulation. This same principal is why a balaclava is also warmer than a beanie, because wind and cold is kept off your neck.
That said, the hoodie buff LOOKS gimmicky as shiite. Then I started reading a bit more about it. The hood is made of windstopper which is essentially just Gen 1 goretex. So it will be windproof, mildly breathable, and highly water resistant (when clean it will probably only let water in through the seams, unfortunately looks like there may be one on the very top of the hood). There's a thin microfiber layer to cover your nose and mouth that will block some wind but won't impede breathing much. Finally the integrated neck gaiter will provide some warmth too. The product definitely isn't gimmicky, looks aside. That said I'm not sure about the placement of the windstopper. I like wind protection around both my ears (which get really painful in a freezing wind) and my neck for warmth. The buff cyclone gives me that option, but not the hoodie. Still the hoodie may be easier to use in balaclava mode than a normal buff since it's more specifically designed.
If it looks like it will fit your needs I wouldn't worry about it being gimmicky and turning out a dud. I own an original buff, a wool buff, and the cyclone buff and all of them have been great. I think the company has a good feel for headwear so there's probably a niche purpose for the hoodie version (I'm thinking it's A LOT easier to configure as a balaclava which would be nice in colder conditions).
Also they have two hooded buffs. The HOOD buff looks more technical, ie the hood is more form fitting (and probably lighter) whereas the HOODIE buff looks to have a larger hood and they state it's a bit more fashionable. So depends on your tastes but I would lean towards the regular HOOD buff (or the cyclone which can look really ugly but works well for me!)