I've been using DiskWrangler for several years, and I think it's fantastic.
It allows me to keep all the stuff I work on in one convenient location for launching apps and documents. It's a huge convenience for me as I hate to have to mouse around to find files all the time, and Spotlight doesn't do a good enough job of isolating the different versions of files and applications I keep on my hard drive. That reminds me... another great use of DiskWrangler is that I can launch the same file with different applications, or different versions of the same app. DiskWrangler lets me launch files with a few keystrokes, or mouse clicks if I happen to be mousing at the time. But when I'm in the middle of working at the keyboard, it's a real convenience to be able to switch and open apps and documents without having to go reach for the mouse. Another great convenience is the launcher Sets it offers. I have a set of startup apps that I fire up when I log in to my user account. (I know I could add them to my account startup items, but this gives me the option to skip that lengthy process on the rare occasion when I don't need them all running immediately, at the cost of a couple of keystrokes.)
I occasionally use DiskWrangler's Browser functions to do things with invisible files and stuff like that. It's handy when you need it. I haven't really used the other features that much to comment on them.