This has to be my new favorite mod to show off to people. The HDMI is clean and has no noticeable input lag. That doesn't mean it won't have some small problems though. The GBA uses a 3:2 aspect ratio for games and it appears as though the HDMI slightly squashes the output to be 4:3. I didn't notice it on every game, but sometimes circles looked a bit more like vertical ellipses (See the pokeball in the image). The stereo audio, while crisp and clean even without an amp, was inverted. The 2 wires were hooked up correctly and I couldn't find documentation on what would happen if they were mismatched, so your mileage may vary. Small issue as I can just swap my TV's left and right audio outputs or play with mono. The install wasn't too bad but the HDMI board is a tight fit with 40 pin IPS kits. I have the V2 IPS from HHL and I had to stretch and mash the ribbon cable to get it to barely reach the connector on the HDMI board. However, if you are decent with soldering, the two audio wires and the 3 IPS wires (brightness) are no big deal. Modding the shell was super easy, just go slow and steady with a file and your hole will look like it was meant to be there.
Overall, I am pleased with this mod despite its few issues, and I would recommend it to any hardcore GBA enthusiast.

Works well no issues was easy enough to hook up and solder in

Easy to install, you get a clean 720p signal, and it's just fun. I use it on hotel TVs when I'm traveling for work. I absolutely recommend this to anyone.

I installed this mod shortly after installing an IPS LCD in my GBA, and the process was fairly simple, like a passthrough connection.

One piece of advice I can offer if you're using a 3D printed bracket to keep your LCD in place, is to break off the small piece that goes over the flex cable for your LCD, as it gets in the way when you're trying to close up the unit. Maybe this was just because of how I did it, I don't know.

Game Boy Advance HDMI Converter

This was fairly easy to install minus the cutting of a shell (hopefully one someone will make a cut shell for these).
As far as the video out, it was great to be able to use HDMI but having no choice in how it is displayed is disappointing. If they aren't going to allow any choices it really needs to be at the correct aspect ratio and fill the majority of the screen or at least give a scaling option.

I hope they could make this have a consolizer version where you have Bluetooth (maybe no internal screen needed) so you can leave it next to the TV and use a controller (mainly the SNES controller for the Switch or any 8bitdo controller).