Anyone using Roomba commercial vacuums in your library? Or any other robot type of vacuum cleaners...

Wondering about capacity of cleaners, how well they hold up over time, and if they really save staff time on vacuuming?

We're looking for something to just take the edge off the vacuuming work load. We have new carpet and want to keep it in tip-top shape and it seems that there just isn't enough staff time to keep up... 

Any advice to share?