What is the SmartPi?
The SmartPi is an extension board to turn a Raspberry Pi into a smart energy meter. All the parts, including the enclosure, are available separately but it is also possible to buy a fully assembled device (discussed here). The assembled version is built on a Raspberry Pi 3 model B.

The SmartPi can measure current (up to 100 A, with a hardware modification up to 300 A is possible), voltage (up to 400 V) and frequency on three phases plus neutral and calculate several flavors of power (active, reactive & apparent) and consumption.

The software is open source and available from GitHub.

The evaluation SmartPi came with three current sensors.

The web interface showed three currents, three voltages and three frequencies.

Conclusion
The SmartPi is a Raspberry Pi extension board for makers, not a consumer product. The software supporting it is basic — three-phase only, configuration over SSH —, documentation is insufficient. People without RPi or Linux experience will be lost quickly.

On the other hand, if you are looking for a platform on which to build yourself a smart energy consumption metering system, the SmartPi definitely is a good start.

Arduino AC measurements
http://www.epanorama.net/newepa/2015/03/15/arduino-ac-measurements/