I took a FRER yesterday and a few hours later saw a line, but obviously shouldn't take that as a positive.
I've only got cheap One Step ones at the moment but they say they can read 10uml.
I did one with FMU and nothing.
Felt queasy all damn day so did another test when I got home. I thought i saw a line, but it disappeared?
Here are the photos.
The inverted one us of the 5min one