The biggest differences are:

  1. The ioStack is powered by 4.5–28V DC whereas the Omnimeters are powered by 110–480V AC.
  2. The ioStack has four pulse inputs whereas the v.4 Omnimeters have three
  3. The ioStack offers the additional ability to get data from up to four 1-Wire sensors, four analog sensors, two I2C sensors, and control up to four relays. The v.4 Omnimeters offer the ability to meter most single and three phase electrical system and also control up to two relays.
  4. The ioStack has some additional functionality when it comes to its pulse inputs.  In addition to the pulse input counts and pulse input states (which the Omnimeter Pulse also counts), the ioStack also has runtime timers on the pulse inputs and pulse rates on the pulse inputs.

FeaturesioStackOmnimeter pulse v.4
Input Power
4.5–28V DC
110–480V AC
Pulse Inputs43
Control Outputs
Analog Sensor Inputs40
1-Wire Sensor Inputs40
I2C Sensor Inputs
Single Phase Electric MeterNoYes
Three Phase Electric MeterNoYes