I have 4 Tie-Fast units. After I learned the Uni knot as well as the Egg Loop and Snell I've never used them for anything but clippers. The Double Uni works great to join line to line so no tool needed. The finished Nail Knot and the Uni are the same knot with no tool needed. Most of the guys making their own leader (tippets) use the blood knot.
The Tie fast works great. I use it all the time when I am on the River and have to tie tippet to my leader, or on a really bad day leader to my fly line. I use the Double Nail Knot and it has never failed me and is super easy to tie with this tool. You can also use a drinking straw and cut it in the same way that that the Tie-fast is made..and its cheap. I useally keep a couple extras made out of staws in my pack just in case I drop anotherone into the river.
There is a much easier way. Tie a 4 wrap Uni Knot out of 20 lb. Dacron fly line backing. No tool and you can do it in your sleep. The Uni Knot is a must know anyway so you might as well use it. We've been discussing it on the Salmon/Steelhead board.
There's some way to put in a stop knot on your line that will go thru the guides but it will keep a float from going above it, allowing you to put your bait further below the surface than the lenght of your rod. A FishSniffer article says to first tie a "nail" knot in your line. Can't find out what a nail knot is. Any help?