The top and bottom piece snap together fairly well, but a couple screws in the mounting holes will make sure it doesn't come apart. The reset button is tapered to be pressed in once and never fall out. The windows to the input ports are very small and WILL make plugging wires in a bit of a pain, but they work well to hold the wires in place and take some stress off of the ports.
I've found this case to work well with Arduino and Elegoo UNO R3, but please do let me know if I can modify anything to make for a better fit. You're welcome to modify the design as you wish using the included Solidworks file. All that I ask is that you let me know if you find it useful!