I have followed the profiling procedure and it worked. Then - without moving the meters - I took a reading on a 100% white. It was matching +/- 0.001 or less, so happy days. Then I enabled a previously-made calibration under Windows - so my 100% white patch changed a little - and took another measure. Now the meters are not reading the same values. Not far away but about 0.004 difference.
I thought the same, so I repeated the measurements several times on both instruments but the delta was always the same - x and y almost spot on on the 100% patch used for calibration, but not spot on other patches.
The reason why I'm being picky on 0.004 is that I have created a colorimeter profile on DisplayCAL and the outcome of a calibration is a reddish greyscale, that's when I started checking with the Jeti!
In the end I got a more pleasant result by
1. Using a spectral calibration under DisplayCAL
2. manually compensating the white target: checking with the Jeti, it was reading x=+0.005 off, so I dialed a x=-0.005 on the white coordinates field and the final result was almost spot on.
That said, looking at DisplayCAL logs the software is failing most of the targets during the second pass (it's trying more than 10 times), that may explain the inaccuracy. Ok, it's not the best setup but I'm surprised it cannot reach an accurate greyscale.