Chances are he got taken. Most "electric superchargers" are just marine fans mounted in an intake tube. They don't move nearly enough air to actually make any boost, and in most cases only choke off the air supply.
There are higher quality products out there, but none of them really come close to the performance of an actual supercharger or turbocharger. If the thing looks like a POS, it probably is. If it's actually a good design the manufacturer shouldn't have any problem coughing up a dyno sheet or other evidence that it works (or was at least tested).