HI, HendrikDC - I think I can answer most of your questions.
How do I find working with Jump Remote Desktop: I use Jump on my Mac and on my iPad Air and iPad Pro. Sometimes, Micrososft Remote Desktop will not connect to one or more of our Windows servers at work. It reports that it has certificate problems, and that's it - but oddly enough, when I attempt the same connection in Jump, it goes through perfectly. Jump has never failed to connect and stay connected.
Did it have a proper Retina resolution As opposed to the 1024x769 resolution on MS Remote Desktop? I'm not sure if I can answer this accurately. I can say that when I selected full screen, the Windows machine screen perfectly conformed to the iPad's screen with no odd, out-of-bounds scrolling. In that sense, it felt like it worked exactly as it should. I don't remember MS RD having resolution issues, but then again, it's been awhile. I do remember an issue where I would have to drag the screen around to get to the left and right corners in MS Desktop. That does not happen with Jump. Jump fits.
Same thing when remote-controlling an iMac, by the way - sort of. Jump fits the entire iMac screen in the iPad Pro window letter-box style - like a move. The whole screen is there and everything is legible and usable. I'm not sure if that answers your Retina question.
Did you experience any lag between the physical mouse movements and the pointer on the screen? No, it was very responsive. I laughed because I felt like I was using a Surface.
Overbal did you experience any issues compared to working directly on a Windows laptop or MacBook? No. I'm honestly extremely delighted it works so well.
I hope the feedback helped. I'd be interested in hearing how it works for you.
--David