I have tried it & think it is a very nice brushless shaving gel. Nice performance but not like the one experienced after applying hot lather with a soft and firm badger brush. When in a pinch, or for a variation on your theme, it can be used. But not my daily cup of tea! Or even monthly...
I use it off and on. It does give a smooth shave, at least for me no irritaion, razor burn neither. I also use Pararso and Jack Black too. Its kind of expensive though but does last a good while when used in rotation.
I'm a fan of most of the Billy products I've tried. I use the hydroplane for traveling or mornings when I wake up too late... I really like the sucker punch face scrub.
I would say that it is NOT very concentrated. I remember using a quarter sized amount to get good coverage for one pass. The cream (gel, really) becomes transparent when you apply it, sort of like Jack Black Beard Lube and Sharps, so it's hard to tell how much you have on your skin.
The gel is also kind of goopy and a little difficult to mix with water. In this regard, a brushless gel like Sharps is easier to work with.
Regardless of its characteristics, I shaved with Billy Jealousy with my DE like I did with other lather creams and soaps, and I got a good shave. It's a good product to use if you don't have a brush or if you are in a pinch.