The undefined and empty items are not used by the game anymore, TftD recycled them into the new drill weapons. I'd like the editor to keep that functionality. NKF posted some experiences with editing those items somewhere...
edit: here we go
Yeah, I want to keep those things in there because I want to make it easier for a person who's using a modded game to be able to mod their stuff as well. I will eventually have the ability to use text and images from the actual game you have installed itself so if you have mods, they'll show up in the editor no problem. Putting those things in your craft and in your base don't actually cause a problem, they just don't show up. Finishing what is being worked on is a really good idea, and I will try to get that functionality in there before I release the full version, but it'll take a bit of work so I may push it off to the next iteration if it takes too long.
The psi stuff isn't going to be put behind a tab because I don't think anyone who's not played the game will do editing first. Also, if you're using an editor to beat the game quicker, you're not going to get the full game anyway, and won't care about a spoiler. If everyone disagrees then I can totally do that, but my thinking is that anyone using this program is going to not really care about a spoiler for their own reason.
As to why there's an installer, I mostly just wanted to know if I could create one and I thought it would be easier if there was just an automated process, but maybe that was wrong. I wanted to get the idea across that you don't have to have it installed in your x-com directory because you can locate an x-com game anywhere on your computer. Classes start tomorrow for me, so I'm desperately trying to get out as many bugs as I can and finish the unitref.dat stuff and then do a real release of version 3.0. Please do let me know if there are any bugs you find.