I liked the doubler well enough, especially considering the form factor/weight. The AI Focus (which I still have) is bigger, bulkier, and with less EQ controls. It does have more power and that nifty HP filter on both channels.
The EA is definitely brighter and has a bit of that "sheen" that the Headway has. Sometimes that's a useful thing, sometimes I prefer the darker sound. Right now, I prefer the PJB super flightcase to both of the heads mentioned here, but it's not really a fair comparison because it's a combo and there's no way to tell how much of the mojo that amp has is the preamp/amp itself, and how much is the cabinet design, which I find brilliant for DB. I should also mention that I was only able to try the doubler through one or two wizzy 10 speakers, that I have never gotten to try a wizzy m-line, and that I have never tried the new AI Ten-2, so all of this should be taken with a grain of salt.
The soundclips tell the story better than words for me, though. The PJB sound can be found on the Nachbar recordings on my site except for "Love For Sale" which is the EA doubler; the links to the doubler recordings are at the end of the article linked in this thread; and I was able to dig up a recording of the AI head from an old thread Invalid Link Removed. To me, they're all workable, but i do have my preferences. Different people would likely have different opinions.