I use LunaDisplay. I have both the Thunderbolt dongle and the USB-C version.
I used it for a while to use my iPad Pro as an external screen for my MacBook Pro (Intel).
I used it recently to use my MacBook Pro (Intel) as an added screen for my Mac Studio (M series).
Note that you have to buy the dongle version for the host system, not the remote.
I found it works fine, and the key benefit is using older systems that don’t support Sidecar or other solutions, and also the Mac to Mac mode. (And I think they have added some Windows to Mac support too.)
I did not find it working well enough for editing video. I wanted to use the Luna-screen as a full screen display for the video (“program monitor” in Premiere Pro-speak). It was too slow in refreshing.
It works ok for static or not fast refreshing images such as menus, general productivity apps, etc.
One thing, and this is totally my own opinion, unproven, I think the hardware dongles are misleading. They do not magically provide hardware-level performance versus the pure software monitor sharing solutions such as DuetDisplay.
My analysis is that the dongle is primarily a fake monitor handshake to trick macOS into using a hardware buffer for secondary monitor. Much like the dummy HDMI plugs for running a Mac Mini headless.
After setup, the main data flow of mirroring the screen is done over Wi-Fi or wired USB and via software drivers. No magic hardware acceleration.
I would say try out Duet Display or similar products and if the performance is ok, but you want more features, flexibility in setup, and perhaps some incremental performance, then go for the Luna Display dongle.