Washed them a bit in a bucket with liquid soap and water. Tried to depress each piston to check if they are seized or not, I thought it would take great force, but to my surprise it's doable by a thumb without too much force - brake fluid came out as a result from hose - so I guess it's all good! Rubber dust boots look good too - I don't even think it needs changing (but may still do it while I'm at it)
What is new to me is how simple and reliable construction is: 2 pins, 1 clip and that's it - you can take out pads even without removing caliper on the car. Brilliant design by Brembo (I guess all bbk are like that lol)
Caliper has 2 bleeding valves covered by rubber caps. I checked them and they look like new! Interesting that pads are quite big and pretty much 80% left - tempting to just reuse everything
Also took off brake line from caliper - came off easily, just needed 9/16 wrench (isn't German cars in metric guys? I'm new to this). So far my impression is that it's safe to buy something like this (mine is from 60k miles salvage car 2012 E70 X5M). These calipers are build to last IMHO, worst case scenario you will need to change worn rubber boot - that's it