As much as these bag vacs rate high on consumer reports, and as tempting as they sound to keep the machine clean, I would be leaving a ton of soil in the carpet if I switched. Its one thing to run a vacuum over a carpet and say; " Ok, its clean. I just vacuumed it !" But its quite a different level to say, "Ok, I KNOW I've gotten all I can from this carpet!"
A bag vac just doesn't allow you to see when the soil is removed as much as a clear canister bagless vac can. I don't know how many times I've worked over and over on a door entrance, or a spot with gyp-rock dust or carpet deodorizer powder, where the dust just keeps pouring in. The first pass just loosened it up. A bag vac, regardless of its cfm or rpm, would have left 90% of it in the carpet.
But, if its all you got, better to use it than to think the truck is going to get it all. Thats an even bigger misconception!
Dust taken from a room and hall JUST vacuumed by owner before I arrived.
One of 14 canisters of carpet deodourizing powder removed from a 200sf living room. Carpet "looked" as clean as it does in the picture. The powder was hiding
(nasty stuff!!) A bag vac wouldn't have touched it and I would have never known it was there.