WiNRADiO (and pretty much any good analyzer) is a software/hardware solution that allows you to see a large block of the frequency spectrum (much larger than just wireless mic areas) and see _Everything_ that is going on (how to interpret it is a different, and very long, lesson). From that you can make judgments of where to place your radio signals. An "auto-frequency finder" basically just quickly scans through the available frequencies and finds the quietest for use. While this is surely helpful, it is not what a dedicated frequency scanner is. That being said, for average needs - a dedicated frequency scanner is not normally needed.
In any case, Sabine claims they have 70 and change channels available for use. The problem here can be interference, and that is why Sabine built in the frequency finder(s). Your average Wireless Access point will consume 11 of those channels. Two of them 22 channels. Your average 2.4Ghz phone will take 3 of those channels, and a spread spectrum phone about 8~10 (this information all from Sabine themselves)
So, lets just say you do a gig in an area where there are 3 access points, two cordless phones and a wireless video camera all in operating distance (which can be up to 1~2 hundred feet for a lot of those technologies, more for some and less for others) you could be down to 5~10 channels for use.
Now, while that is a worse case scenario, and in part true of any radio based system, you need to think about it.
I will admit however that it is a nice system, and most definitely deserves consideration.