Just in case you missed it, our friend Zeke of Zeke Shoots had an opportunity to test these out and chat with Mark Krebs during the 2016 Bullpup Shoot hosted by Manticore Arms up at The Site.
TFB story below.
Krebs Custom Interchangeable Muzzle System (IMS) for AK rifles is now available through their website at $90. It allows to have 16.25″ barrel length and still be able to attach different muzzle devices without significantly increasing the overall length (except when used with suppressors)…
Source: The Firearm Blog