I've tried corresponding with the makers of the VA, asking the same question as you. I never got an answer; they said the timing advance was not a set number, but varied according to one or more factors (engine rpm, load, etc. ). But nobody would even give me a hint as to the "average" amount of advance, or even advance at some given condition such as "2000 rpm, light load". Secondly, my experience with the VA-HO model (for the ETH) was that it gave a very nice, smooth power increase, but if it impacted the mileage at all it was nowhere near the 2 to 3 mpg some have reported, at least not on my truck. I keep meticulous records of every gallon purchased and average speed on each tank, so I don't make this statement lightly. If there had been a 1 mpg increase (or better), I would have seen it. Other trucks may be different, this is just my personal experience. I'm not bad-mouthing the product at all; I'm just saying there is a reason that VA publishes HP and torque gains but does not claim any specific mpg gain. (I have not yet tried the EZ. )
I recommend you consider these products for the power, and if you get an mpg gain, consider that as just a bonus, but don't count on it paying for the product. JOMO