I don't think you'll find any negative reviews about the tune, and it looks like you'll be seeing some owner impressions over the next few days. I know there are a couple owners on here who have the flash pro installed already and they were simply waiting for the calibration to be released online.
Let us know how your Accord feels after the stage 3 tune! Hondata is pretty much the tuner to go to for more power and their reviews seems pretty positive so far, though I've never tried their products.
I wish there was a little more information available on the stock gauge cluster. It kind of sucks that those going for an aftermarket tune are also going to have to download some paid apps in order to get a proper overview of the boost gauge. At least there is a workaround with android auto that doesn't require any changes to the stock infotainment system.
The only problem with adding secondary gauges, is that requires getting into the dash and splicing wires. For some that may be something that they can do on their own, but I personally wouldn't be comfortable doing it myself. Not to mention adding gauges can clutter up the dash, but I do like the setups that place them along the A pillar.