I don't know, is that thing designed for a MB (Pro)? I'd say it's bound to be ineffective since the fans are on the bottom and macbooks only have a 'grid' at the latch of the monitor. There are other laptops that have holes in the bottom casing too, it would be much more effective on those cases, I'd wager.
Why do you need a cooling anyway? The two unibodies over here never really get all that hot (13"-ers).