It's busted as hell but I really like it. It's a simple change in the overall gameplay but having to look out for this quick popup and being rewarded with a free heavy attack is such a neat addition to the experience.
I've pretty much switched to Naramon on all frames because of it.
I haven't gotten around to play with it much yet, but yeah I quite like it so far as well. Great to have bit more depth and power too for melee.
I did have turn down the whatever effect intensity setting though, it was hard for me to see the flash on a more busy missions.
I've got a really nice tennokai setup with a paracesis, Tek Adarza, and magus aggress. Melee feels way more dynamic and way less stressful than the bloodrush meta; I can swap to melee whenever I want and do sick combos, rather than being obligated to keep the normal attacks going forever. I'm a fan.