You got it! Just figure how long it would take to glue and nail furring strips and how many of them would curl up and break the bond, and how you would have to cut the insulation to fit between the strips. Now subtract that from the time it would take to screw the siding on. Use a good hammer-drill and a driver drill and it goes really quickly. Now count the call backs to repair the strips and skipped insulation and the screws are like money in the bank. I didn't have a single call back on that job.