Overall
The case is hard plastic with a foam interior. One clear negative is the latch is very hard to open so you need strong fingers or maybe a modification to make it a bit easier to open. When empty the middle of the case will flex if you push hard the edges wont.
The case will prevent damage ...

I wanted to get the hama suggested but i couldnt find a supplier anywhere near me. Amzon wanted £20
I ended up ordering an orico 3.5hdd stackable case its a hard plastic case so should be nice and strong £7
I googled the standard size of the zumo xt and a 3.5 hdd this was the result.

HDD 147mm x ...