The Miyoo Mini+ is probably obsolete in favor of the TrimUI Brick.
TL;DR: There are a lot of glowing reviews for the Miyoo Mini+ out there. But based on my experience, as a newcomer to handheld emulation, the TrimUI Brick outshines the Miyoo Mini+, and it's not even close. It might be time to start recommending the Brick over the Mini+
So for background, I've gamed on emulators for decades now, on everything from a 486 to a Raspberry Pi, and most recently on the Steam Deck, which I use as a console plugged into my TV (because that device is huge). But after a stint with my old GBC, I realized how much I enjoyed getting away from the computer/TV, and how much I enjoy the shape of a vertical handheld. So I decided to look into emulation handhelds with a vertical form factor. There were a couple obvious, highly recommended options, and I went for both: the TrimUI Brick and the Miyoo Mini+. The idea was that I'd tinker with whatever folks came up with for the Brick, and use the Mini+ for reliable gaming in the meantime. But after a few days with both, I think I'm going to put the Mini+ in a drawer an forget about it. Even with the current state of Knulli, the Brick is just so much nicer to play. My reasons are detailed below.
The shoulder buttons. Looking at the two systems, I thought the sloping buttons of the Mini+ might be more comfortable to use. But it turns out that the Mini+ shoulder buttons aren't easy to get a grip on. My hand doesn't want to rest there while not actively pressing a button, and that leads to a lot of shuffling my hand around the device. On the other hand, the Brick's square keycaps create a notch for the fingers to rest in and stabalize the device whether or not the buttons are being pressed. While playing Metroid Fusion on the Brick, I was suprised to find myself pressing and/or holding one or both shoulder buttons effortlessly, without losing my grip on the device, and without having to think about it. Likewise, strafing in F-Zero is comfortable and reliable. Meanwhile, I found myself fumbling the Mini+ more than I'd like on both games, especially when using the left shoulder button with the d-pad.
The speakers. I didn't expect the speakers on either device to be great, and they aren't. But I want to be able to hear my games anyway, and not necessarily with earbuds in. So I use those speakers. And it is shockingly easy to fully cover the speaker on the Mini+, essentially muting the device. My right hand changes position fairly often when pressing face buttons, and especially when hitting a shoulder button, which makes the bottom-right corner of the device (where the speaker is) quite inconvenient to avoid. Meanwhile, the Brick's speakers are a little more centrally located. I don't usually cover them accidentally, and if I do cover one, there's still the other. Consquently, anything I want to play with sound is much better played on the Brick.
The screen. I've bounced off my old Advance/DS games recently due to poor eyesight. So I thought the additional size of the screen on the Mini+ might be a better choice for regular play. I'd even considered an Anbernic 40xxv for the 4 inch screen. But it turns out that the better resolution on the Brick more than makes up for the 0.3 inches of screen size the Mini+ has on it. The Brick is easier for me to see, and more beautiful besides. Naturally, I'd still like a larger screen on either of these devices, and I'm still eying an Anbernic device for this reason. But between the Mini+ and the Brick, the Brick is easily the more useful screen, even factoring in size.
General performance. I've only noticed perforance issues with the Mini+ when messing with the DS emulator. And I've had trouble configuring the DS emulator for the Brick on Knulli. But what I've seen of DS games playing on the Brick, they're enough smoother that I'll find or wait for better CFW on the Brick before playing them on the Mini+. Or even just avoid the Mini+'s stutter on a different platform entirely. Furthermore, the hope of using Portmaster on the Brick is really exciting, and there's just not the same chance of that for the Mini+.
The face buttons. The Mini+ buttons are bigger, a pleasant glossy texture, and non-clicky. This should be an easy win for the Mini+. But they have two flaws that overshadow the ways in which they are superior. First, the ABXY buttons are bulbous and and protrude significantly even when fully pressed down. Consequently, they sort of dig into my thumb when I'm playing a racing game, or any game that has me mashing or holding down a button for some time. What's more, both the face buttons and the d-pad are positioned much lower on the Mini+ than the Brick. Consequently, they're further from the device's center of gravity, meaning it's more difficult to hold or balance the device while using those buttons. Meanwhile, the Brick's buttons are quite high on the device, very near the screen. This isn't always ideal, as I sometimes inadvertantly touch the screen and leave a fingerpint. But their position contributes massively to being able to hold the device comfortably for long periods of time. I've done a couple 2-3 hour sessions with modest breaks on Metroid Fusion, and been more comfortable than with any handheld I've owned (so that's a comparison to the Mini+, the Deck, and most Nintendo handhelds, past and present).
All this means that the Brick is easier to hold, easier to control, easier to see, easier to hear, and more performant besides. No slander towards the Mini+. The device is cute and setup was slightly easier than for the Brick. And where the Brick is better, the Mini+ isn't always bad. If I didn't have a Brick, I'd probably be largely satisfied with the Mini+. Furthermore, the Mini+ cost me about $15 less than the Brick, all told. But the Brick is worth much more than $15 more to me, even with the current state of the software. So if you ask me, the Brick should take over as the obvious first recommendation of the two in the vertical space.