I tried an Apexi piggyback but my problem was the stock ECU... couldn't get it to read the speedo from the tranny, along with some other errors, and it affected the VTEC.
If your stock ECU works fine then just get an Apexi. Your right, it just tricks the stock ECU, he can adjust the VTEC to come in earlier and make a smoother powerband. It's got a little screen that can show other parameters too, at least at night (can't see in daylight).
I was trying to avoid the cost of the AEM Series 2 Plug & Play ECU (plus in line windband UEGO Controller) but now wish I would of just bit the bullet a lot sooner. There are so many options with this aftermarket unit... timing, traction control etc... The AEM is pretty much the first step in getting the most out of engine preformance mods (and necessary for blower/turbo). I probably should of gotten the wideband fuel/air gauge but didn't want to add a gauge to my dash (that's what I pay a tuner for and I wouldn't know what I was looking at anyway).
You could go with Hondata (basically an unlocked Acura RSX ECU) if you don't plan a lot of mods (and want DMV to think its all stock) but you have to change some minor engine parts so the cost actually might be higher than AEM.
With a 2006 or later motor, you don't need to replace the ECU. Hondata makes a controller that you can plug in and make changes to the stock ECU.
http://www.scienceofspeed.com/products/engine_performance_products/S2000/Hondata/FlashPro/