I'm looking at getting the Mortar too but sadly there's not much info out there on it. It seems to be coming out kinda late to the 450 chipset party. You can, however, check out Tomahawk reviews as they are fairly similar, with similar feature sets.
https://www.youtube.com/watch?v=lxtrHDJUMt4
https://www.youtube.com/watch?v=MWGzmbbimPw&t=17s
Mortar has the same VRM design as Tomahawk, a 4x2 CPU VCore design with a large well finned heatsink, so it should be just as cool running even for a 2700X. The features are pretty good, with 2 USB3.1 gen2, one being a Ty. C. But the really cool thing is it has two M.2 slots. Being a B450 chip it will be PCIEx4 gen 2 but at least you've the ability to put a second NVME drive in to image your system over for upgrades.
On paper, at least, it has one of the better B450 VRM designs but it's definitely not top-end like you can find on a few X470 boards (none in the mATX form, however.). You're not interested in overclocking so that shouldn't be an issue, but it should handle a 2700X very well. Otherwise, the only real cons I can see are it's not a 470 chipset so you don't get to SLI or the other connectivity features needing more high-bandwidth PCIe slots and the like. It also doesn't have 'high-end' audio, if that's important, but it doesn't have the bottom end Realtek codec either.
The last negative is it's RGB'd so unfortunately you'll have to take that with the price even if you don't use it. At least the on-board backlight LED's are subdued, which could be considered a positive considering what else is in the marketplace.
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