I bought it for the convenience. One of my local HBS (brewbros) can do a great crush so it was more about buying in bulk and brewing when I feel like it instead of having crushed grains sitting and waiting for a nice day to brew.
It's not as well made as I thought it would be. In hindsight I think I would buy a Monster Mill and cobble together the hopper and mount it in a cart.
As samc said, it mostly depends on how good (or poor) the crush is at your LHBS. With my grains crushed by the store I usually got 60% efficiency. First batch with the Barley Crusher it jumped to around 75% and I'm within 1 or 2 percent of that every time. I'm happy with 75%, but I'm still tempted to crank it down a bit and go for 80 or 85%.
It's also so much more convenient and cheaper for me to buy in bulk. I can do less planning ahead and brew anytime I get the urge, since I always have enough for several different styles.
Bottom line - pull the trigger, you won't regret it.
I have a JSP (non adjustable) rather than a Barley Crusher.
It replace a Corona mill.
Before that I bought my grains pre-crushed.
Pre-crushed, Conona'd, or JSP'd, I never noticed any difference in efficiency, but I've noticed a big difference in cost and time. (I may have been lucky with my pre-crushed grains.)