I downloaded that hoping it would have a readme and it did. To quote one of its lines: "- What's Specfix? Simple: It allows you to spectate matches from the player's perspective (just like you would in Quake). You always could do this in UT by typing behindview 0 at console, but there were several problems. Specfix fixes those problems."

Problems? What problems! Tell me what you are fixing! And then it goes on to list a whole bunch of its own bugs (seven in total), and brushes them off as no big deal. But they seem enough to scare me away from trying it.

The only spectator glitch I can think of is one mentioned in this mutator's readme, and that is that the armor values are zero. I know of this glitch and I fixed it in my own spectator class, but you can only see this correction if you have chosen to use the custom HUD I have made available. Please see this post for how to use it:
http://www.birdieman.com/cgi-bin/bin260/YaBB.pl?num=1416079929

However this post has reminded me of something I want to try for spectators, splitting the screen in four to spectator multiple players at once.

I guess I should have mentioned that this makes no difference unless you spectate in "behindview 0" (which I always do)

I'll do that video comparison this weekend, you'll see the differences are obvious.