Reader mystery: Vintage postcards with metal frames

A Papergreat reader named Molly has checked in with a postcard mystery for us to explore. Sending a batch of photos, she writes:

"My great-grandmother started my addiction to postcards when she bequeathed to me her small collection. Over 1,000 cards later, with a cutoff year of 1910, I am still buggered by 23 metal framed, 3" x 4" postcards. The paper part is also thicker than the regular postcards of that era. Most include a foldout easel on the back. ... I can't seem to find any like them anywhere ... nor any info about them. Obviously they are rare, indeed. Any internet links you may have to help me would be appreciated."

As you can see from one of Molly's images, these directions appear on the back of her cards: "Pull out the easel back or wall hanger with the point of a knife." With a little Google luck, I discovered that the Simplicity Company of Chicago sold metal-framed postcards in the first decade of the 20th century. But they might not have been the only company doing so.

Regarding Simplicity, this news item appears in the March 23, 1907, issue of The American Stationer, a trade magazine:

Notice to Post Card DealersThe Simplicity Company, Chicago, is sending the following notice to the trade:

"A recent article published by newspapers throughout the country, in relation to a ruling made by the Postmaster General, wherein it declares that metal cards are not longer mailable unless sent in an enevlope [sic], might possibly lead dealers to a wrong conclusion as to our metal frame post cards, we herewith call your attention to a copy of a ruling made us by the Hon. Fred A. Busse, postmaster at Chicago, and dated March 8, 1907, several days after the publication of the article referred to above, and which reads as follows:

The Simplicity Company,
307-321 Dearborn Street,
Chicago, Illinois.
Sirs:—
Yours of the 7th March (F.J.W.) received. Metal bordered cards like sample submitted are mailable at the fourth-class rate of postage, i.e., 1 cent for each ounce or fraction thereof, when the message thereon is entirely in print. If, however, the message is wholly or partially in writing the cards referrred to will be subject to postage at the fire-class [sic] rate, i.e., 2 cents for each ounce or fraction thereof.
Respectfully,
Fred A. Busse, Postmaster.

The above is an exact copy of the postmaster's letter to us."

So it appears that at least one company might have encountered some early difficulty with the marketing and mailing of metal-framed postcards, which might have contributed to their rarity. According to Metropostcard.com, The Simplicity Company was in business from 1906 to 1927 and moved to Grand Rapids, Michigan, around 1909 after getting its start in Chicago. But Metropostcard makes no mention of metal frames.

Here are some more images that Molly sent along. If anyone else has any more information or leads on this mystery, let us know!