To be clear, I am not opposed to the use of EQ to reduce the one or two lowest modal peaks in a room. Conventional broadband bass traps are less effective once you get below about 50 or 60 Hz. So even if an equalizer or DSP device cannot reduce ringing, just lowering a peak's level and the amount of its ringing (if not reducing the decay time) improves the sound in a very real way. Indeed, I have 40 RealTraps in my own living room home theater, but I also use the one-band cut-only EQ built into my SVS PB12-Plus/2 subwoofer to tame the worst modal peak around 40 Hz by a few dB. Top
The MultEQ is certainly effective as an equalizer, and since it adjusts itself automatically it has the potential to be easy to install and setup correctly. However, Audyssey does not sell this device to end users, but rather requires you to hire a professional installer. It is also very expensive for an equalizer.
In contrast, for about $150 you can buy a Behringer parametric equalizer and use the freeware Room EQ Wizard software to automatically control the EQ from your own computer. Even if you buy a separate computer just for the EQ, the total cost is still lower and you "own" the hardware and can recalibrate your system whenever you want without paying a professional installer. The Room EQ Wizard also performs a very thorough room analysis, showing much more information than the software bundled with the Audyssey MultEQ.
Finally, I'd like to reiterate a point I have made many times in my acoustics articles and web forum posts. The frequency response in domestic size rooms changes drastically over very small distances, even at low frequencies. Therefore, unlike bass traps that always improve all locations, any EQ that improves the response at one location is sure to make it worse elsewhere, even a few inches away