Is Menu-minipanels reliable to make a mega menu
Menu Minipanels looks like a good choice.

An alternative you might want to try for a simple 'mega menu' is the Mega Menus module. Worked well for me, once I had my settings and CSS sorted out. See also this answer for lots more mega menu options...

Finally, regarding performance, since Menu Minipanels uses Panels you will have full control over caching of individual panes within it. The performance burden can therefore be significantly reduced.