I'm gonna try to help here. I've been told this doesn't come off well but, pre-emptive warning, i'm not trying to be a dick.
You're not quite comprehending what's being said. Yes, some bikes get upwards of 20% better fuel economy. No, you'll probably not get 20% better fueling. It will be improved though because, from the factory, the fueling is off due to EPA regulations. Getting it tuned and running a happy air fuel ratio is much better for the bike and will increase your MPG because your engine is performing it's internal combustion more efficiently.
You may fall into the trap that many do which is, "i got my ecu flashed and now my fuel economy went down" when in reality, your ecu got flashed and you're riding more aggressively because the bikes so much more fun to ride. fuel economy is tied to your wrist as much as your tune.
No, not all bikes do. 12% vs 20% throttle to maintain cruising speed is an example of the difference in post tune vs pre tune, some bikes get more some bikes get less. it may sound weird off but some bikes will go from 80hp to 100hp, with nothing wrong, just needed tuning. some bikes, go from 80hp to 82hp, but below peak it picked up 10hp along the power curve. every bikes different, i dont know what mpg the new zx10rs are getting post flash.
v twins are the worst, and benefit the most from a tune, you should see the difference in cruisers and ducati's, it's hard to believe people ride them untuned, that's how bad they can be. the triples and fours aren't as bad.
Realize he's summing up thousands of dyno tunes on thousands of bikes of every make and model and modifications etc.
For a real example of experience you're asking about: On one of my street bikes, 2009 Yamaha FZ1, my MPG went from 30-32mpg to 35-37mpg with hypermiling on the freeway up near 38-40mpg, after Nels flashed the ECU.
the benefits you can't read about on a good ecu flash like 2wdw is the smoothness and consistency of the power delivery, engine braking, throttle control etc. to me, that's the benefit of the ecu flash, getting the bike running as it should, mileage be damned. if you wanted a commuter you don't pick a 1000cc superbike, you just gotta pony up for the gas, that's just part of the package, performance comes with a price
here's how it goes, you're gonna love it, you're getting a product from one of the best ecu tuners out there with more ecu's flashed than any other dealer out there. check the facebook reviews
, yelp reviews
and he's running a tax return sale right now anyway, 10% off the $349 cost of the flash