Hi
I've had the same issues with early firmware however 8C0 has been stable and no crashing, with current uptime at 14 days.
The 7 version firmware did have a pretty bad memory leak which caused it to reboot every few hours or a lot sooner if using the Web UI. This was fixed in verson 8C0, so I would double check your version is reported as 8C0 under the Firmware upgrade page. It is also worth resetting to defaults and re-entering the configuration if you hadn't done this already when going from 7 to 8.
Also check the power supply is rated at 12 volt 2 amps. Modems/routers with dual radios and high speed ac Wi-Fi draw quite a lot of power in bursts, so if not using the correct power supply will appear to work okay most of the time but then seemingly reboot. Also enable the Log and check after a reboot if the cause of the reboot is shown.
Also I would suggest clearing your browser cache folder after any firmware update to ensure any scripts from the embedded web server are re-downloaded to avoid using out of date ones.
I do agree what you say about the Web UI, it is very slow at times and could be better.
Regards
Phil