I can see how having a few pre-defined options would be convenient, but these kinds of features don't scale very well. I personally probably interact with a dozen different gas stations, and maybe a dozen different additives or whatever. That's very manageable. But we need to think about everyone that will use Fuelly across the globe. Then we're suddenly managing *every* gas station brand and *every* additive brand and it becomes our job to track those and present them to the user. And do we put them all in a single list? Choosing from a dozen or so is easy, but choosing from hundreds is a pain.
One option is to let the user build their own pre-defined list of options. I believe only a few power-users would take advantage of that, so that means complicating the interface in some way for what I think would be a rarely-used feature.
I understand your point about more metrics for comparison, but I'm not sure you'd find much meaningful difference between fuel-ups marked "Texaco" vs. "Shell" for example, because of the way we gather data. You fuel-up at Shell, and Fuelly is calculating the MPG for gas you burned from Texaco. I think Fuelly is better at giving you a sense of the big picture.
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