Hey guys, first time Rad owner, first post...for people that may not know, the Topeak rear bag adapter does work on the factory basket frame. I'm so glad that I didn't have to spend hundreds again just for a convenience. I used blue loctite just to make sure nothing rattles loose.
I did need to find which bolt pattern I wanted and move the arms. I found it easiest to remove the arm brackets and open to full extension then from underneath, mount the arms to the main track. Just a little bit of caution here as the Rad bag frame tubes are beefy, the adapter arms won't sit flush back on the Topeak frame however being plastic they flex... just be careful when tightening to not break (part of the reason I used locite) because it's all plastic, not aluminum like the OE Topeak rack but I think it will do it's one simple job... for $25 I'm not going to complain.