Options for a jack to keep in the rear hatch....

I prefer the KISS system. Keep It Simple Stupid. For my overland build ML I chose an inexpensive hydraulic bottle jack. They are much more stable and capable than the scissor jacks (like the OEM). Simple bottle jacks are also incredibly reliable. Throw it in the back of your ML and 30 years from now it will still work. While neat, I would never trust a 12 volt electric jack to work when I needed it. Electric motors fail and I simply could not trust it long term.