mantis is imo infinitely better than rackbrute... and less ugly, but that's just personal opinion...
mantis is a little bit bigger (20hp/row), has no rack wart, has a super clean power supply (up to video rates - which is low MHz, not just KHz needed for audio), more power on the 12v rail (which is where you need the most)... and because of the size almost always works out cheaper per hp...
nb the 12v power is zoned so you have to pay a bit of attention plugging modules in (each zone is 1A, so no more than 750mA draw plugged in to each zone)
it might be a good idea if you watched your way through at least the first post or so of this thread: https://www.modwiggler.com/forum/viewtopic.php?t=106396
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities