I can't help you with respect to make or model of a scan tool, but if your build includes a PCM controlled engine or powertrain, I would highly recommend it.

For the average guy, probably not. But for a guy building a Coyote powered car in his own garage, hell yes. It would be an invaluable tool for diagnostics from first start through to years down the road. Frankly, I don't know if I would do a Coyote without access to a scan tool.