Personally picked him up during Kazekage treasures for 180 seals.

I've been running him with him, Bee (which I also picked up) and a chakara gainer (Mabui/Shikamaru Makeout Paradise), for massive damage. PVE/GNW/RANKED has been a breeze for me easily overpowering people much higher than my combat power.

I do recall seeing a video of a team with Tendo & Gaara, and Gaaras damage was "comparable", but someone double-check for me on this, however him running him on l6 Nin Magas and l8 ghost tactics and he's just nasty when his mystery goes off.

Kage treasures came out shortly, I had a million regrets but 2 weeks in, no one has gotten him on my server yet and some people are close to drawing a super rare already, which makes me feel like he was worth it and he's not as common as some of the other rare pulls in Kage.

There's a hype over Mei but personally I would consider him the best rare pull from Kage if you can fully utilize him.