After reading reviews and comparisons of the two tools, I had decided on getting the Hold n Fold. Some reviewers didn't like the alignment groove and other small problems with the Etch Mate.
However, I ended up getting the Etch Mate anyway because it was the only one I ever saw on sale here in Japan! It cost about $75 US.
And I love it! I see no problems with the alignment groove or any other of the gripes I had read about. It's a great tool that takes the stress out of folding PE. And it's actually quite fun to use!
On top of all that, it's a beautiful piece of machining. Excellent quality.