When I designed my bench I intentionally left off any end vise because I wanted to remain somewhat true to an English style bench and I knew that I was going to make another bench (probably this summer).
Well, I started to second guess myself and decided to take a look at retro-fitting an end-vise of some sort, to the end of my new bench. The most appealing would have been a wagon vise. Bottom line is that because of my bench's little overhang (10"), the leg and top stretcher gets into the way of most every type of vise I considered. I am OK with all that and am back to being happy with what I have. I still intend to build another bench. You can't have too many clamps, right? And that is all a bench is.
Anyway, to get to the point, I re-visited Hovarter's vises. I had looked at his website a year or two ago after Chris Schwarz wrote a blog about it. Len started his business just a couple of years ago. He has a very innovative mechanism that really should be seen to be appreciated. See his website.
I like his wagon vise and really wanted to incorporate it, but as I mentioned above, I don't have the room. What I like about it over Benchcrafted's, is that it only requires a very narrow slot in the top besides it being a quick release. Len and I have traded emails recently and I got a good feeling about his desire to help me. I wanted to help him and also everyone here by out by mentioning his vises. I would recommend investigating what he has. The simplicity of his design looks like it also translates into a simple installation. I probably will be going with one his vises when I build my next bench.