Lumu pro light meter for iPhone

Did anyone try the Lumu Pro light meter for the iPhone?
I really like the idea of having a spot and an incident meter all in one super small device, I use both a lot for 4x5 large format photography and this device would make room in my travel backpack.

Did anyone try it? Is it any good?
How is the spot meter? Is it accurate enough and the angle small enough (~1°)? Could use with the Zone System?

I have been using that for ages with all my cameras that did not have a miter on them. It is very accurate even on spot metering. Now that I have learned to estimate the exposure by myself, I do not use it that much, but only on tricky conditions or when my mind simply doesn't get through it.
Lumu can be calibrated. If you own a camera with a spot meter known to be accurate, you can use it to bring Lumu down to your preference.

Just a side note: I'm not using the sensor but only the Lumu app (which is free) to measure 90% of my exposures.