Used once - wanted a vac system forever - and I loved this. A must have for modern ABS systems, or if there's concern your brake booster has air in it (expensive to replace if it does).
My only limitation was my small 2.5 gallon compressor. Performance fell off as my pressure dropped.
If you are buying this, I am assuming you probably know what you're doing, but just remember to leave it running as you finish and tighten your bleeder on the caliper to keep air from being sucked back in. Another tip: the hose is really long, and I cut mine short, because I will never have my cars in such a position that the bleeder is very high or far from the caliper, and a shorter hose means less time to evacuate fluid to the container.