Just installed the MX4. Looks pretty good. Couple of comments.
1) Don't install outside when it's below 30C (hard to do in Michigan in the winter).
2) Broke the bed plugs while removing them (probably because it was damn cold). Ordered new ones from amazon $24.
3) Missing a screw, but had an extra "nut" for the snap locks.
4) Don't like the "raw edge" of the extrusion in the back - see pic. Looking for suggestions.
5) A little tight to close the tailgate.
6) Waiting for the weather to warm up to hopefully "flatten" some of the weather strips.
7) Quality of the drilled holes a little rough.
Overall, I like it..... ridiculously easy to install. Great youtube vids to help.