I own the cordless peanut, and it's good, but it's more of a detailer than anything. I'll use it to trim my mustache, between my nose and mustache, or between my sideburns and my ears.

I use the Oster Professional Octane Cordless Clipper to trim the bulk of the beard. The battery lasts forever - like months - and it's very powerful and solidly constructed.

I would recommend getting the ceramic blades though as the standard metal ones can run pretty hot.