I have the hot magnum, and Iam extremely impressed with it, iam not sure how it would do on a 45 though, I have a 29. Its completly silent (the tank is a foot away from the base of my bed) it was easy to setup I have the media container half full of carbon and half full of biomax and have two layers of filter floss and the flow rate is still very strong, I noticed no differance going from just a single layer of filter floss with no media in it. Italso comes with a water polishing catridge, which I generally use for 24 hours at a time and it made my tank immaculate, its a fine fine cotton mesh type filter, that takes out micron sized particles (this is the reason why I bought this filter, once a week or so I will give it a 24-48 hour cycle with the polishing filter)
if you are going to use two filters I would definatly recomend this as one of them, if you want just one filter you might need something a bit bigger, although it claims up to 55gal, I as most ppl like to over filter by at least double of the stated claims....