Here is my comparison between mylar X3 and X3i.
Yes, bass is definately stronger than original x3. But the bass is not tight and deep. A bit muddy to my liking. The X3i had better Detail, separation also good and wider soundstage as well.
Sound isolation is definately more better with double flange. Very good for rather noisy surroundin like crowded area, on airplane. Conclusion, a well worthy upgrade from original x3.