Ok here today, and mounted on my bad weather beater:
The Wald 139 basket. It's a fairly large basket, measuring 15.5" wide by 11" long on the inside bottom. It is 6" deep. I'm glad I did not go with the smaller 137, because I know it would have ended up being too small for carrying more than one or two packages around now.
Looked around the garage for a "maximum" test load, and this old set of portable studio lights just about fills the basket:
Weight just over 10lbs, didn't seem to have much effect on handling, at least not on this laid back frame.
The quality of the basket itself is fine. The mounting is a little bit dubious though.
The handle bar clamps are made for 1" handle bars. If you're mounting to older smaller diameter bars they include some rubber shims to take up the difference. Works fine right now, but I'm wondering if the rubber will compress over time.
The "legs" seem sort of flimsy to me, they bolt onto two tabs on the bottom of the basket, the tabs don't seem particularly sturdy and the screws are pretty thin. It's probably good enough for holding a heavy load when the bike isn't moving, but I'm concerned about whether this arrangement is strong enough for side to side forces.
If you're familiar with old Wald baskets then you may remember that the bottom of the legs have three holes for different mounting heights, and that they mount to the front axel. Well, apparently no longer. There is one large hole and one small hole per leg, the large one for axel mounting, and the small one for eyelet mounting. To level the basket out one has to fiddle with the handlebar clamps. If you have a tall bike or tall handlebars this is actually pretty good because it means the overall arrangement is stronger than it used to be. But if you have a short bike it means positioning the handle bar clamps forward, where they probably don't do much for supporting weight.
Anyway on my test ride round the block, I did not hear any rattles from the basket, and it seemed to handle the 10lbs. weight of the box with no problem.