The leather loop feels like plastic, because underneath each "bump" is a magnet or metal piece which allows the strap to be magnetized.
The milanese loop is not scratchy at all. Surprisingly, it's the most comfortable strap that I have tried. Even more comfortable than the sport band, as it is infinitely adjustable (don't have to choose between 2 holes where there is 1-2mm difference between them), and that the sport band leaves a gap at the top where the band is stiffer towards the area where it connects to the watch.
I have read that some hairy guys have hairs getting snagged in the milanese loop, so that is something to take into consideration. I have no hair on my arm/wrist, so it is not a problem for me.
Milanese has been comfortable for most of the day. There have been 1-2 times where I have had to loosen the strap to readjust, but I've done that with all my watches.
I think the take-home is: the milanese is just as comfortable as the leather straps. But try-on if you have a hairy wrist to make sure it doesn't pull.