I use an air at work and i have a DeWalt at home. Although the work one has multiple torque/speed settings, I find the DeWalt do just as good a job as the work one, and you have a bonus of being portable. Sure the batteries dont last a long time, but I bought a kit that came with 2 batteries so one is on standby all the time. If you buy the DeWalt, make sure you get the heavy duty batteries.
And 600 bucks is a great buy considering I paid 800 a few years ago.