The unofficial test mentioned was only a small improvement for city/highway mileage -- a meager step from ~18.2 to 21.3 mpg. I would want to see more than a 20% improvement with my car's fuel consumption. For example, if my mileage went from an average of 23 mpg to 30 mpg, I would be satisfied, but a jump of 23 to 25 isn't substantial. Although I must admit, that almost any consistent improvement is better than nothing.
Doing some calculations for my car, at 2 mpg more, a tank would net me roughly 35 more miles or, on average, another half-day of driving before I need to fill up. Since I fill up roughly every seven days, half a day per week should net me something like an extra 3.7 weeks per year. At roughly $52.00 per fill-up, I would save ~$190.00 per year. If I go a step further, the USD8,850.00 hydrogen box would pay for itself in 46.5 years. I think I'll pass, unless there is some major fuel conservation improvement. Which, I should add, could easily happen within the next year, or even six-months.