I've got a late 2013 12" MBP. That's got 4GB RAM, retina screen but it's the base spec.
Scrubbing through isn't too bad but rendering and exporting can take time, and the longer and more complex the edit is (especially layers) can take time, but as far as editing up, it's fine.
Motion 5 however, plays back in its preview window and nearly half speed. I have to import to FCPX to test stuff I've made and tweak based on that. Not too much of an issue if you're making stuff that flips between the workflow nicely, but if you were tinkering a clip you might need to export as a clip to check, although that doesn't take too long to export a short one, and for testing you can export in 480p to speed things up too.