It is supposed to be used with a USB power bank to become a mobile power supply. Which actually works fine!
You can also use it to split one output port of your standard power supply into two isolated outputs.
Pros:
- small, lightweight and portable
- get any input from 5 to 18V and transforms into 2x 9V output
Cons:
- The "filtered" output does not seems to reduce any noise compared to a "non filtered", non-isolated PS
- The max output is not 800 mA divided by both outputs, but 400mA in each output so keep this in mind you cannot connect a 450 mA pedal it will not get power enough.
- The hassle of connecting one wire between the power bank and the Engl Powertap might not pay off. I have a Rockboard powerbank and it is direct and you get way more power 2x 1000mA you can power your board directly (assuming you do not have 5 Strymon pedals on it :)
Concluding
I believe getting a Rockboard or Haley Benton power bank is a better option for mobility, but if you only need it to power 1-4 low power pedals it works great.