Overall a great find, if the construction holds up it's a winner.
The flip up design is what really sold me on this vs competitors, i don't really need a diopter but still it's nice to have. and the optics look quite good along with edge to edge view-ability of the LCD. You will get fogging but as you can see i poked a hole at the bottom to help with air circulation. I will likely just buy some anti fog spray to seal the issue.
The build quality
Yes, it's all plastic except for the optics, though it doesn't feel cheap. The plastic is just thin enough to have some flexibility, and just thick enough to feel sturdy. The hinge will certainly be the weak point, it has some play to it,and im sure i could rip it out if i wanted to. I don't consider this much of an issue though, because i treat my equipment well. If you're the type of person to throw your things around, then buy something all metal and suck up the extra cost. Even if the hinge were to break on this one, you could still just glue it in place and have a perfectly usable non-flip up viewfinder.
The way an LCD viewfinder attaches is where all the manufacturers try to be clever. This unit, does not try to be clever, and i like that about it. It's a basic sticky frame that attaches to the camera, and the viewfinder just snaps into place. No magnets. The snap in feels solid, and the stickyframe feels satisfyingly stuck to the camera. You have a little release lever/button to get it off the camera which works just fine. It's simple, it doesn't get in the way, it just works. I hate other viewfinders which add mounting brackets and whatnot, i don't like extra bulk, and that's where this one excels.
The soft rubber eyepiece is nice, but just barely. Other rubbers are larger and more form fitting, this one is not, but is just enough to be comfortable and block the light. You can rotate it around for left or right use, or take it off altogether. The optics are nice and clear, but no anti-fog, so grab a bottle of defog spray. You also get a diopter, a very important feature for many, and while it's a bit clunky in operation, it gets the job done. You also get a neck stracp attachment so you can keep the unit handy but unattached.
There are the cheap crappy viewfinders, the expensive viewfinders, and the in betweeners who get the job done. This one is actually cheap and gets the job done. You can spend hundreds of dollars on higher end units, and some of them are totally worth it. But if you're trying to save some cash, a unit like this will absolutely work.