The concept of electric supercharger is not a scam at all but obviously it has some serious limitations. First of all if you expect a 250cfm electric blower to give the performance of an engine driven supercharger with way over 1500cfm deliverig at 2-5psi, you will be dissapointed. If you are thinking of an electric supercharger, the first thing you should look at is your engine capacity, in terms of cfm at maximum rpm. If that exceeds 250cfm or whatever the promised capacity of you electric blower, then you can safely drop the whole idea of an electric supercharger. If that is within limits, you might get some benifis depending on how efficiently your engine can produce horsepower at given degree of compression. You would have better hope of success if your engine is EFI with a MAP or MAF sensor.

All in all I should say if you plan to try the 250cfm blower your engine better be a 4cyl one with 1.5L or less, with EFI having a MAP or MAF sensor. Otherwise the idea of cheap power will be hopeless, because higher capacity engine would call for a bigger blower, darwing more current and hence more power losses. If whatever the useful power left convers to more HP or at least more HP at lower engine rpm, then you will be lucky but I would not take that risk.