Build quality
The DX50 has the edge here. Upon first receiving the X3, I have to admit that I was disappointed that the build quality isn’t even close to the quality of my E17. I realize James told us in advance that the X3 design is several years old (it was put on hiatus for over a year due to subcontractor supply problems) and that we should not expect more up-to-date E17-like build quality, but I still felt the disappointment. The E17’s beautiful brushed aluminum case is sublime. The quality of the case is first-rate and it feels like it was milled from a solid aluminum block. Not so with the X3. From a distance, the X3 appears to be built like the E17, but that is only in appearance. The case is actually plastic, and not particularly sturdy feeling plastic either. There are thin sheets of brushed aluminum bonded to the top and bottom to give the appearance of an aluminum case, but once you hold it in your hand, the illusion ends there. I don’t think it would survive even a short fall onto a concrete floor very well. I keep my X3 is in the silicone sleeve at all times. It is a bit weird looking, but I feel much more comfortable with some protection.
In comparison, the DX50 is more than a bit better. While still nowhere near the quality of the E17’s construction, the DX50 just feels more solid. The plastic body is much thicker, better finished, and feels more durable. There is also more (and thicker) aluminum used in the outer shell. The DX50 feels more solid in the hand, and it would probably survive an accidental drop better than the X3.