I haven't tried C2 yet. I did have some Pepsi Edge and I thought it was pretty decent. Not quite as good as the real stuff, not quite as fakey tasting as diet.
I kinda feel like these products are useless though. Sure, people will buy them, but here's why I don't care much about them. I've been on a low-carb diet since the beginning of the year (have lost 35 pounds and maintained my new weight so naysayers can shuddup pre-emptively). Sugared soda has a LOT of sugar, which means it has a lot of carbs, which means I've been drinking diet. Diet sodas have artificial sweeteners and generally no carbs. C2 and Pepsi Edge are targeted at low-carb dieters, but they still have sugar in them. A can of Pepsi Edge has 13 carbs, I can't find the info for C2 but I imagine it's similar. For someone starting a low-carb diet, a couple cans a day can wreck your results. Usually in the first phase, you aim for around 25 grams of carbohydrates a day, total. Later on (like when maintaining weight) you could probably do ok with it, but why bother? If I feel like having something sugary, I'll go drink a real Coke or Pepsi, since it's only an occasional thing and even cleaning out the Old Country Buffet will not make you fat if you only do it once a month. I'd rather not spend the carbs on a halfway better Coke if I could use them on some food I actually want to eat instead.
I'm just not sure who this appeals to. People who exercise a lot or have uber-metabolisms will continue to drink the real stuff because it tastes better and they don't care about calories. People who are seriously dieting (probably a very small subset of all those claiming to be on a diet) will continue to drink the pure diet stuff due to lack of calories and sugar, even if these new ones do taste somewhat better. Maybe some people will buy it because it's a happy compromise between regular and diet, but I dunno. Maybe people who used to get a Big Mac, fries, and a diet Coke will get a C2 instead. Products like this will potentially ruin the low carb diet because the manufacturers slap things like "less sugar, lower carbs!" on them, even though they are not really LOW carb nor should they be a regular part of a low carb diet. And consumers are generally too stupid to understand things like this, so they follow the hype/marketing and blame the diet (which they weren't following) for their lack of success. Hrmph.