The performance on my unit seems a lot better, it's smoother and the few niggling bugs I had seem to of been ironed out, I haven't had a dropped WiFi signal since running 4.4.
Cosmetically, the GEL 3.1.8 update turns it into a different device. The translucent panels, fonts and wallpapers are very pleasing to the eye. The 'okay Google' feature seems to work well, but I'm not sure how much I'll use it.
The battery seems to be running down quicker, but that could be because I'm playing with it more.
If you're comfortable sideloading, I'd go ahead and do it. It appears to be a solid update.