I got my mango Excell today. My thoughts on it:
The taste definitely isn't as strong as watermelon Xtend. The watermelon Xtend tastes good when slightly diluted past the recommended dosage of 2 scoops per 16 oz. The flavoring of the mango Excell is much more subdued than the Xtend (at least at 2 scoops/16oz). I would compare the flavor more to a calorie free, sucralose fruit water drink. You can definitely taste the mango, but it isn't really overpowering like Xtend. The Excell mixes better with far fewer floating specks. Also, I like how the Excell doesn't have artificial colorings like Xtend, since colorings can stain bottles. Also, I like to drink BCAAs during work and it looks somewhat silly when you're drinking pink liquid out of a bottle that has lots of floating white stuff for the first 30 minutes (especially since I work in a somewhat professional setting).
In my opinion, watermelon Xtend is a bit over-the-top in terms of flavor. It makes a good drink in those situations where you really want a stronger taste (for instance, during a meal). But during other times such as when you just want to drink water, Excell makes a good replacement since the flavor isn't too strong. This is especially pronounced during workouts. I'm used to drinking plain water during workouts and the watermelon Xtend is just too sweet in my opinion. I'm guessing the Excell is better suited for workouts, but I will find out the next time I take it to the gym.