I got the Preonic as a gift, so I can't post in the actual reviews section because I'm not technically a verified buyer. Support said I can post my thoughts here though.
I love this thing. I may actually go a size down and get a Planck next time they're available. I've been using it for about a week and a half. I guess I'll share some of the thoughts that stick out the most to me.
The fact that it's ortholinear is both easier and harder to get used to than you think. On the one hand, all the keys are in roughly the same relative location to each other and your fingers as they have been on every other board you've used, but conversely the habits you've developed from aiming in the physical space they occupy will throw you for a loop for the whole first day. For instance, 0 (the number) is right between O (the letter) and P, and I've been hitting it with my ring finger my whole life. On this it's exactly above the P, so I had started out typing hundreds of 199s. B is exactly centered on a standard keyboard, so I've been pressing it with my right index finger since I learned how to type on one. On this though, it's much closer to my left hand. I'm still not 199% on that key either.
You think you'll miss the other keys, but you won't. They're still all right here. I HIGHLY advise mapping it out in a way that makes sense to you. I spent the time it took to ship to me on the QMK configurator brainstorming the layout that I realize now I've always wanted. Apostrophe is now where the semicolon was, while semicolon is now down here next to my spacebar with hyphen opposite, I have a 10-key pad right under JKL, and playback controls on the arrows. It took me less than an afternoon to learn how to change my hand movement habits, and now when I;m back on a :normal: keyboard I make a lot of silly mistakes for the first few minutes before my hands readjust.
Now for the building experience:
As others have said this kit does not come with switches. I got Kailh box browns for a little piece of mind keeping the keycaps on and the potential dirt and water out; also because it says the hot-swap sockets are Kailh. I know they're not part of the drop, but I will warn anyone interested in them that they grab stems VERY tightly. Almost a struggle to get them on sometimes.
I've never built or worked on anything smaller than a desktop computer that wasn't made of brightly colored plastic. This was easy. From the time the parts got here to the first sentence I typed was less than 2 hours. I will say the top plate has some sharp edges you have to be mindful of, and the tolerances are very tight, so your fingers might get a little sore from pushing the switches in. Also there's no "click" or anything when the switch pins seat into the sockets, so you just kind of have to use your best judgement and let the screws do the rest. Once everything has been tightened down it feels better than a store-bought product.
The acrylic case is exclusive to this drop, and definitely worth waiting for. It will match everything, and the frosted texture keeps it from looking tacky like many transparent electronics (also from getting scratched). It's got some weight to it, so I have no fear that it's going to just crack at the screws or anything.
Flashing firmware (remapping keys) is super easy on Windows thanks to all the GUI tools available. As much planning as I put into it, I still had to make a few tweaks once I actually put everything into practice. I intend to get deeper into some of the lighting and audio features later. I'm not much of a coder or anything, but so far the community has been super helpful at a moment's notice. I'm not the least bit nervous about starting.
I've wanted a smaller keyboard ever since I moved and had to get a smaller desk, but needing a numpad for things like IP addresses and the like has always stopped me. When I saw this and recognized my beloved 4x5 grid right there in the potential palm of my hand I thought there was hope for a compromise. This isn't a compromise; it's just the better way to type.