Just read this whole thread, can't figure out why some of you guys think it's an inaccurate effect when stereo itself is an inaccurate effect but sounds good.
A lot depends on just how much 'inaccuracy' one can tolerate, and what's important to the listener. As you correctly point out, stereo itself is an 'inaccurate effect' inasmuch as it's an attempt to recreate a full dimensional soundfield from two adjacently spaced sources. Generally it leaves a center hole that is often not 'covered' very well-- depending a lot on recording technique, but also the radiation pattern of the loudspeakers in combination with the listening room.
In the early days of stereo reproduction this sonic artifact was readily apparent to pretty much anyone, as everyone was coming from monophonic which was a 'point source'. With widely spaced speakers this 'defect' was more prevalent, and sometimes made over by the use of a center speaker and a 'blend' channel. Paul Klipsch's 'solution' was one of the most widely known work around. I think David Hafler had one, and his preamps always featured a 'blend' control to minimize this peculiar stereo artifact.
As far as stereo goes, in the 1980s there were a lot of serious people seriously predicting the death of two channel reproduction due to the introduction of sophisticated surround systems which were said to help to eliminate inherent limitations of two speaker hi-fi. As we know, that prediction has not happened.
Stereo is mixed for stereo speakers. I heard the original SDA line and it was one of those things that sounded impressive but quickly sounded "fake" because it trashed the stereo image in favor of something different and unexpected by the mastering engineers. I had the same feeling about Bose 901's; impressive at first, but having everything spread across the entire front wall was just too much. If you like the effect that's cool; it is subjective like so many things audio. Personally if I had them I'd like an easy way to switch it off since I listen to a lot of solo and small-group music for which the SDA effect just didn't sound right to me.
The 'problem' with the Polk 'solution' as
@DonH56 points out it that the effect is both widely room dependent
and recording dependent. I've not heard it, but the reviews I've read indicate that it's effect is quite variable, sometimes good, sometimes not so good--so it's not a 'one size fits all' solution.
In an earlier comment
@Kal Rubinson points out that the design requires a lot of amplifier power inasmuch as half the drivers are cancelling a part of the other driver's signal. So all things being equal it's a more expensive solution than, say, the Carver 'sonic hologram' electronic box, the latter having the benefit of being able to be switched off if you don't like it, or don't want to use it on a particular recording.
All that said, and as I always say, loudspeakers are the really only major subjective piece of gear left in the the hi-fi chain, so if Polk floats your boat, and if you have the dollars and space for SDA, then that'd be the way to go. Either that or buy a used Carver box and see how that goes for you.