I had a cut off launched and hit my thumb. After a trip to the ER and few months it is now back to normal and 100% usable again. I will not post the photos but it was mangled and I never hit the blade. Just a little wedge hit my thumb an ripped off the nail. After that I went on a quest to design a better jig, I kept improving it till I have what I now use. It's still possible to get hurt but I think the risks are much less now.

One flaw I see with your design is that the cutoff stays on the sled and can vibrate across into the path of the blade. If you forget and pull it back it can... no will launch that cutoff. I think that is what happened to me. Honestly I am not 100% sure. I felt something and looked down and my thumb was hamburger.

If you want to improve it, start by get both hands on the left side of the blade. With both hands on the left side it also forces you to stand out of line with the blade. Then I would also cut the sled off at the blade and let the cutoff fall onto the table. That way you don't drag it into the backside of the blade which will throw it at you at around 100 mph! If you don't believe it I will show you what it did to my thumb.

Here is a photo of what I ended up with. This was the last prototype and I did clean it up some by replacing the blocks with one piece and that actually fit on the sled. I have used it a lot and so far it works perfect. I am very happy with it and don't really see much else I can do to improve it.

Here is the thread.
http://www.kayakforum.com/cgi-bin/Building/index.cgi/page/1/md/read/id/192077/sbj/tools-improved-strip-scarf-jig/