I tried it on GOG KOTOR 1.03.

It "works". In that you get widescreen resolution support.

But it is flaky as hell IMO, but that isn't Kotor issue, it's a FWS issue.

You need multiple restarts for it to take effect. Sometimes it still comes up not quite right.

Even when I got it to work, my game went from completely stable to crashing and corrupting save files.

Eventually I deleted everything FWS and Kotor, and reinstalled KOTOR Clean, and it went back to be a stable game that I could play.

Widescreen is a "nice to have" features, but it isn't worth trading it for hassles/crashing/corrupt saves.

Flawless Widescreen is far from 'flawless'. In fact, I couldn't get it to work on my system whatsoever (Win7), so I went with the UniWS information here, and it works perfectly. Follow the instructions TO THE LETTER!

Everything Peter has said is correct. It does take multiple reloads to get it to work sometimes but it always does eventually - the most attempts I had to make was 7 but it usually works on the 2nd or 3rd attempt. There are also issues with the occasional crash that can corrupt your save files - I've found that it is usually the quick save file that gets corrupted following a crash so be sure to do some hard saves if you decide to use FWS. It can also crash when attempting to do a hard save which will also corrupt that particular save slot so I have 2 hard save slots that I alternate between. Having these 2 save slots along with the quick save and autosave slots has meant that I've never had to replay more than a few minutes when I've had a crash.

That all does sound like a lot of hassle I know. I guess it depends how much having the widescreen means to you. For me I'm using FWS to be able to play the game in ultrawide at 3440x1440 so the contrast between that and 4:3 ratio is huge and worth the regular saves I have to make as I progress through the game.