Ultimately, yeah, mostly just looking for a nice secure place to hold the small collection of junk I always take on a ride - tool, tube, co2(2), micropump. The contents of my old saddle bag. I can carry one bottle in the frame and one on the body, and phone on the body. Alternatively I could just keep using a pencil case in the jersey pocket, but would kinda like to get some out of jersey pockets.
The Milk$$ is pretty tight on frame space to put the tool stuff, and while I do have a set of cage mounts on the DT, I feel meh about a cage there.
Also, while 2 bottle is enough this time of year for a 2ish hour ride, having a bladder might be better for the same 2hrs this summer.