This looks like a pretty nice pistol but these guys wanted it real bad.

https://www.gunbroker.com/Item/864757677

$5,525.00  At that price point I would sell mine...

55 hundred Bucks .... DAMN !
Don't know that much (if any at all) about the Bren Ten, but a 10 Round Magazine ?
Wasn't the Bren manufactured before the HiCap Ban ?
A Double Stack (CZ 75 sized) Grip Frame and Magazine, and you only got 10 Rounds ?
With this Frame and Mag, it would easily handle a min of 12 Rounds
CZ 75 sized Mags:

The Bren Ten was designed 40 years ago. 

This was way before the need for high capacity craze had come into vogue.  I am sure that the designers thought that 10 rounds of 10mm should be more than enough.

Many still do.

They probably thought 10X10 had a nice ring to it.

I imagine their goal was to keep the grip width and circumference aligned with the hallowed M1911 Col. Cooper was so fond of.  However, as the Witness line of guns has shown, you can achieve that goal with much more reserve ammo.

And while I agree that 10 rounds of 10mm is enough to resolve 99.9% of social problems, I also hear Neil Armstrong in my head..."If I had my choice, I would take more fuel."

I'll opt for the thinner grips.   

With other calibers I feel capacity gets more important, in my opinion.

And I thought the guns were bringing big money.  It appears to be a dual caliber mag also which is less desirable also.

  https://www.gunbroker.com/Item/865319611

Wow!