hi, I will play UU1 with Underworld Exporter Unity engine,
So, Underworld Exporter is works pretty well?
it's mean, error or crush, bug, some other problem and issue.
I hope, at least did'n any deadly problem until finish this game.
I want hear more advices or tip.

i have never tried using the Underworld Exporter, so i cannot say how well it works.

an alternative to consider is my UltimaHacks patch (for UW1 and UW2), which adds mouselook and some other features to the original form of the game:

https://github.com/JohnGlassmyer/UltimaHacks

the game is fully playable with this patch applied.

some possibly helpful instructions here under "Apply the mouselook patch (Windows GOG.com release)":

https://www.pcgamingwiki.com/wiki/Ultima_Underworld:_The_Stygian_Abyss

I was NOT able to get Underworld Exporter to be stable on my computer system. Your YMMV.

I also recommend running Underworld with the mouselook patch.