These chips work by messing with the IAT signal going to the ECU, tricking it into dumping more/less fuel into the engine at certain points. It shouldn't throw any codes since it does keep the signal within manufacturer specs.
60HP? No way. Maybe 10.
4-7 MPG? No. Lower if anything.
Lower emissions? Probably not.
And there is no way it costs 400 bucks. The chip is a very simple micro controller that costs literally a dollar.