I've done some research on user 1M3jtksp1upR33SX1VzeCfH5x9fc6zKykR with a hashrate of 640 Mh/s.
This user is using something called GRIDCHIP GC3355.
"GC3355 is high performance and low power SHA256 processor designed by GRIDCHIP. With advanced technology and highly integrated design."
One chip is 84KH/s and cost is 65.5USD which is equal to about 7616 GC3355 chips.
Total cost of this mining plant is 495 040 USD or more.
He is earning $6,337.53 per day which means his ROI is at 78 days.
Edit: Other sources claim one chip is performing 60 KH/s instead of 84 which means his total investment cost is over whopping number $693333.
78 days only if he gets free electricity...
I know they are low power but it still needs to be accounted for.
Edit: also they guy has 2000mh/s as he had already stated before. only 500-600mh/s is pointed towards middlecoin.