I have some old AR90 speakers that have this feature.

Probably some utility, properly aimed!

Old joke:

A lovely young lass is in the pub, and an old local sheep farmer spies her and chats her up.

"Those are lovely boots, lassie, they must be sheepskin!"

"Why, yes, they are!" she says, "You have a fine eye."

"Yes, I do," says the old man. "In fact, I think your lovely skirt must be made of fine wool!"

"Yes, it is!" she says, "What else can you tell about my clothing?"

He reaches over and grabs her boob, and says, "Well, I can tell this must be felt!"

Ba dump bump.

Through the years I have used some different materials for homemade tweeter diffraction control. I was reading about a speaker Dick Olsher was designing and he was using foam weather stripping around the tweeter. I have tried foam and recently adhesive backed felt furniture protector dots randomly around the tweeter. I am sure the Touchstone Tweeter Surrounds would work nicely. I have to admit that my current speakers are too pretty to cover the front with felt and their angled baffle make the need for diffraction control less important.

I had built a 3-way speaker system with two cabinets for each channel. The bass is in the bottom and the tweeter/midrange units are in a separate cabinet on top, isolated by 2 inches of sponge foam. Each cabinet has a grille with wood frame.

The frame is lined with felt on the inside to manage diffraction around what would have been sharp edges. The tweeter and midrange also has felt around their edges of the 'basket'. The woofer also has a ring of felt that mates with the felt ring on the baffle opening to further reduce diffraction. The baffle board has felt too.

In a pair of other speakers, I also modified the grille covers the same way as well as the board on which the driver is mounted, by adding the felt to reduce diffraction.

Before and after effects are startling - much clearer sound afterwards.

What are you asking, ncdrawl?

Limiting the dispersion characteristics of a tweeter has been around since the LS3/5a back in the mid '70's. Spica covered their entire front baffle in thick wool felt panels with a cut out for the tweeter in a specific shape they felt best for the tweeter they selected. AR did the same as did many who were trying to minimize the problems of a wide dispersion tweeter mating with a narrow dispersion woofer/midrange in a real life room acoustic.

Spica also created very wide baffles for most of their product line which gave the soundwave the effect of operating into a half space infinite baffle. I also had a pair of Boston Acoustics from the mid '70's that did the same thing without the felt - which I later added just before trading out for the Spicas. I used a corrugated foam rubber acoustic treatment panel and attached it to the front baffle with spray on glue.

You can use a few sheets of felt purchased from any hardware store or piece together a few felt squares/rounds from the same source. It will be much less expensive than the aftermarket items you list. Do be aware there are different results to be had with the shape of the space around the tweeter. And you are narrowing the dispersion of the tweeter so the sweet spot will narrow along with the degree of isolation you are after.

Do some searching on the internet to find some of the DIY comparisons of different felt materials/thickness and the best shape for the initial tryout.