The translucent lid is made of plexi-glass. So it's VERY durable, so no worries about that. I believe you can get a solid metal top, but I think the translucent lid adds a nice touch to it because you can see the innards. As far as how thick, it's about a 1/4 inch without breaking out a ruler.
As far as that LD MkV, here's a review:
Review of Little Dot MKV Dual Mono Solid State Headphone Amplifier