I have several HOT Magnums and I like them quite a bit. I mostly use them for mechanical filtration. I prefilter them with a sponge and pack them with floss. They are real workhorses, IMO, and I think they are more effecting mech filters than other HOT filters, even those that purport to filter a higher number of gallons per hour.
You can run the HOT Mag with the micron filter 24/7, but if you have messy fish (e.g., cichlids) they micron will clog too quickly. With less messy fish (e.g., tetras) you could probably run the micron continuously with non problems.
HOT Mags are really well made filters; I think they are sturdier than any other standard HOB filter (e.g., Emperors, Aquaclears).
HTH,
Jim