Bromberg's holder are certainily similar to the BofC holders. If fact, when the two are compared, they appear to be exact.
Several of the BofC holders are slightly warped, perhaps 1/8 of an inch out of true flat. This shouldn't be a problem however.
You are correct about not able to stand alone, they make a poor display method except when flat. Pages for large holders will hold them, but are clunky and easily bashed about.
Weigh is a little much compared to normal note holders, perhaps something that doesn't matter unless moving them around frequently.
Rick