This is a great route. Wonderful views, big gorge for descent, very quiet.
Our montenegro exit permits were checked in the middle of nowhere before the border by the Montenegro police. We had no issues entering Kosovo(no one checked) and there was no fuss leaving Kosovo at another Kosovo official border.
There is info on accursed-mountains.org/important. Strictly speaking you should get a permit from Montenegro and from Kosovo police before entering. You can do this online. We only had the montenegro part.
We got the montenegro police permit via zbulo.org in 5 days. We told them we were crossing from Montenegro to Kosovo and they organised the montenegro part and then told us we should also have the Kosovo one - but that we could not adjust the order. :-(. We could not find a way of ordering the other part on their site anyway (and only found the accursed mountain
website once in Kosovo which was too late). If you wants to use zbulo rather than the plav police i suggest emailing before ordering anything…
The border is officially closed, but with the documents „border permit“ you are allowed to cross the border by foot or bike. You get the border permit at the „border police headquarter“ in Plav.