The real grips were made from plastic and are wider than both Blast-Tech's and Saberfreaks grips. They real fins also have a slight taper, which no replica grips do.
Blast-Tech's grips:
They come in a kit ready to attach to the lightsaber right away. They are already cut to the right size. The underside is curved to fit any 1 1/2" tube (Graflex or MPP) and comes with double-sided tape already attached. The downside is that they are made from rubber, which is inaccurate. The fin can also be slightly deformed from the manufacturing process, but most people don't notice this.
Saberfreak's grips:
You get 10 cm pieces of plastic that you have to cut to the size you want. The underside is flat. They are brown, so you they will have to be painted. However, they are of the correct type of plastic, and some saber grips used in production of Star Wars were also of brown plastic painted black. When I bought them they were slightly cheaper than Blast-Tech's, but the cost evens out if you add in the cost of glue (or tape) and black spray paint.
Personally, I used to use Blast-Tech grips when it was the only option available, but I use Saberfreak's now.
I also got saber grips when I bought my Graflex replica from Parksabers. Parks grips are practically identical to Blast-Tech's except for less deformation. If you are waiting for an USK from Parks, the grips included in the kit are enough for both a Vader and a Luke saber.