I'll chime in here if I may. I recently bought my GX in December and the first thing I did was add CarPlay to it via the Hamilton module. I looked at BeatSonic and Grom, but it looked like the Hamilton kit was easier to install, and I liked that it seemed to have fewer components (just one metal "box" for lack of a better term, and a Bluetooth antenna). Plus, the Hamilton unit was around $300 less than BeatSonic, and basically did the same thing. Anyway, I have installed a couple of head units in my other vehicles, so I figured it shouldn't be that big of a deal. Hamilton has an installation video on YouTube that walks you through the process. You can also watch GXBob's video on how to get to the rear of your radio via removing a lot of the dash. Still, I figured I wouldn't need to do all that because the Hamilton video only has you remove your center console (with your gear shifter removed) and you just need to reroute some wires behind the radio and drop the metal unit under your shifter and you are done. At least that is what I thought initially, but Hamilton changed the wires that came with the unit and I ended up having to remove the upper screen/radio to plug in a wire that runs to that unit, and they did not (at least as of a month or so ago) update their youtube video to explain this.
That was my one gripe in the installation, but the tech support from Hamilton was fantastic. I called their support line and had to leave a message, and I figured it would be a minute before I heard back, but they called back within the hour and emailed me instructions on what I needed to do. Now, I'm used to buying head units at Crutchfields and I would say that Hamilton's support was almost as good as Crutchfields, but typically Crutchfields will call me and walk me through issues on the phone, but Hamilton did a good job with corresponding via email. The unit is working as designed, and I have Apple Car Play and the steering wheel controls still work. Obviously, the screen is still old tech, so that is the biggest limiting factor that I see. I really wish there was a way to drop in the OEM unit that comes with the 2021 GX, but I guess there are too many back-end changes for us to be able to do this. Oh, and one thing that I found very cool about Lexus is that everything is held together with clips that just pop out and pop back in. I mean, there are some bolts that you have to remove, but they are very few. I think both the upper and lower radio units have maybe six bolts holding them in place. That's a far cry from my first Chevy pickup truck I had back in college where I had a bunch of stuff to keep track of when replacing my stereo. All in all, I would recommend the Hamilton unit. I'll circle back in a few months and tell you if my opinion has changed.