I toyed with the idea of a K1200/1300S before buying the Bird. 1200 was out of question due to various issues I read online and 1300 was out of budget. Only saw one 1300 on eBay for 2.5k but was high mileage iirc. Would like to own one someday if I can get over the looks of the rear lol.
Yeah I doubt anybody in my group would recommend the 1200 without a lot of caveats. The 1300 was much improved, but they always had their fun niggles. Like paint that refuses to stay on the engine, or the front wheel carrier, or the rear driveshaft etc. Plus everything else that took me to Bahnstormer fairly frequently that I've since wiped from my memory!
The sports panniers look great though, I always thought mine looked better with them on than without, it completed the rear end properly. Unlike the KTM, which I'm trying to avoid using the panniers on whenever possible!
They are getting on a bit now mind, with the newest being 9-10 years old. And for me at least, I find I can ride the KTM far far more 'progressively' than I could the long low K. Higher wider bars obviously helps, but I think these kinds of bikes have come on a lot since the K. The H2SX that seems to be the spiritual successor to the K, even though it 'feels' pretty similar in geo etc, is also easier to ride fast. But it's also hella expensive!
Mind you, my K1300 friends can mostly keep up when they want to, so I think it was just that I was a lot more rubbish at riding when I had the K! Oh and since I got Track Pack added I'm informed I definitely have the legs out of corners, which helps!
I imagine the Blackbird is far more reliable a proposition than the K, at a similar age and all else being equal. I think most K owners I know have got good value out of their expensive BMW Insured Warranties, or regretted at leisure having chosen not to renew it

.