Well, I just ran this on my DVD rip of Dune (1984), creating a full sized H.264 recording. Compared to Handbrake:
1) It took a bit longer, though it wasn't too bad.
2) It completely locks up the window during conversion, so the concept of queuing is flawed. You CAN add multiple DVD's to begin with, but you cannot add any more until after the encoding.
3) The resulting file was about 50% larger (1.14 vs. 1.7 GB).
4) The resulting file INCLUDED 2 hours and 14 minutes of black bars at the top and bottom AND left and right, creating a 640x480 (i.e., 4x3), slightly laterally squished movie. Top and bottom I get, but left and right?!? Handbrake is 720x272. Apparently, whatever the DVD reports (generally either 640x480 or 720x480), this is the output. No attempt to crop the letterboxing or even to interpret the anamorphic recordings. This is by far the worst offense and a complete and utter show stopper for anyone who rips movies.
5) The resulting video was choppy as hell, at least on my PC. The Handbrake version is butter.
6) Sound was about the same, I think. Everything else sucked so bad I didn't spend much time listening for subtle differences.
7) It is really crazy-easy to use, but I don't find Handbrake all that bad.
8) The interface is pretty darned pretty.
Anyway, one and a 5/6'ths thumbs down from me, FWIW. Only the interface is a winner, and it can't really be deemed a winner since it doesn't allow you to do some really core things. It has been installed and uninstalled in relatively quick succession.
What really needs to happen is for someone with design sense to plunk a for-dummies front end on top of Handbrake. It's not like it isn't 95% command-line anyway. 'Course, that's what needs to happen with 95% of all open-source projects, so what's new?