Yep, what they said.
This, IMHO, is the "best" build to get Mangle ASAP at 50. However, you might prefer picking up Furor sooner if you're on a PvP server or simply go to BG's often as it helps quite a lot in those situations. For pure leveling, I'd personally go straight to Mangle and pick Furor right after that.
You can toy with the build, of course, as there are many variants that might better suit your play style. The most important is to not only take the build and use it, but to also check each talent, see what they affect and understand the impact it will have on your play style.
For example: Shredding Attacks improves the cost of Shred, some kind of backstab attack, so if you don't use it either because of your opening combo or whatnot, you might as well drop that talent in favor of something more appropriate for you. But since you've played Rogue you'll find Cat is very similar and since it'll be your main leveling tool you shouldn't have too much problem.