Anecdote from a ST185 GT4 owner:
Installed the Blitz Access ECU today. It took it a while to get the AFR's to 14.7 at idle. I pretty much babied the car until it started running smoothly. The car runs leaner at lower boost pressures. At 5psi at partial throttle it's still running 14.7. At WOT and 15psi the AFR still hits a little over 10 in the upper rev range. I didn't get much seat time today but it feels like the midrange has improved. Before on the JDM ECU it would run 11ish AFR at 5psi even at light throttle. If you followed with a quick jab to WOT it would plummet below 10. I really need to get this thing on the dyno. I've heard the Blitz is tuned for 100 octane but Japan uses a different method of calculating it. I think 94 octane is the US equivalent. Of course I run 93. I need to get this thing on the dyno.

The mid-range improvement would have been from the engine not drowning in fuel, lol. 

Did that ECU ever end up on the dyno?

I didn't put it on the dyno though it definitely gave the car more grunt.

What is this AFM mod that is mentioned earlier?

Old thread, but thought I'd toss in a few thoughts.
The Blitz Access did come in a custom tune option, but from all reports back then, it was very scarce, and marked accordingly on the ECU. The stock version dyno'd out to a 45 PS power increase on 100RON; I do have the dyno specs somewhere if anyone is interested.
The main changes were, apart from the fuel/speed cut, 17 psi boost and RPM limit,  confined to a re-mapping of the ign advancve curve, and surprisingly enough, a very limited amount of change to the EFI. This was confined to the very upper range of the high boost map, and although extensive in magnitude, limited in range.
Still have both maps I think, but in a previous computer.
You need to run 100RON or an ethanol mix to get the most out of it. On 98 you'd be better to drop static advance back a couple of degrees to keep the advance curve useable.