2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.
I doubt it. It's a solder process, so I wonder if you could do a practical fillet with it. There were home recipees for this kind of thing in the mechanics journals in the old days. I have one somewhere. I guess you could try and see if you could make a rack or something. I think the issue you have to deal with is even if it's in the ballpark, that doesn't mean it is right for the very stiff oversized tubings that are typical in aluminum frames. Maybe it's strong enough for something but what does that something look like?