I did some extensive testing the last 3 days with the U1.
As tiny as it is, The U1 Plus is still a conventional tower that channels air from front to back.
Super true. I have the U9S, NH L9i, Cryorig M9i and am picking up the D9L soon for testing, I will probably stick with the latter as I like its styling more and will throw two redux fans on it. NH L9i, a good cooler of course, performed the worst on idle and load with and without a GPU.
Dual M.2 slot motherboards are a must. The 2.5" SSD mount is on a plate on the front of the case, and so are the air openings on the left side.
Dual M.2 absolutely is not a must, but it would be helpful for sure. One is enough with high capacity dives, but if you have a board with zero, you will be fine nonetheless. The SSD plate on the front is silly in design and somewhat cumbersome but I have tested the front-to-back cooling with it in and out and all results are margin of error. If your cables are managed properly it does not interfere with the small strip of air vents in the front of the case at all as the plate ends something like 5-6 cm away from the strip.
About that plate (the strangest thing in the U1), the mounting on the front is just silly Jonsbo! You can cut off one of the sides of the plate (facing the intake 'strip' if you like so it cannot be seen) if you want to mod it in general, and 2.5" drives can be mounted behind the thing with clearance to mount the plate back on, hiding the drives entirely. Missed opportunity here for them to even use less material. Oh well... Better to leave it off completely for less clutter but it is certainly not a necessity. I chose to leave mine on, I can post some photos of the mod in the next weeks if anyone is interested.
Finally, I've been watching Wiretap's posts on other forums and he confirmed what I was thinking about the Zotac Mini cards. They fit in the U1 Plus like a glove.
Confirmed here too. I put the Zotac 1060 AMP in there. Ultimately (just yesterday) I had to send it back as the back fan was finicky - but it does fit. I will put the EVGA 1060 SC in there instead for more room in general.
The NH-U9s with two fans would be close enough to the front and end of the case, doing double duty of cooling the CPU and acting as intake and exhaust for the U1 Plus.
This is a good idea in general, but there is still some room between the back 92mm fan and the exhaust grill, which does allow a portion of hot air to go swirling around in the case rather than exhaust efficiently. When I tested with the tower, I found a good 92mm on the front (as you noted, close to the intake 'strip') and a good 80mm on the back did a better job with temperatures. I assume because the 80mm fan was close enough to the cooler to suck up the hot air - and since it is screwed to the back of the case - made
sure it got out of the case. Still, the temperature difference was not much, and most noticeable under synthetic stress. It was enough however to persuade me to keep a 92mm/80mm fan split.
Besides, smaller PSU means more space for cabling behind the PSU cover.
Super true again. I love the little metal PSU cover with its anemic screws. If you don't mind a little adhesive, those 3M hooks can be stuck to the top to hold cables up if they are starting to fall below the PSU cover and into view in the glass.