Cannot recommend. - Kinetic Development Group SRX3 Stribog 3in Receiver Extension

First off, it seems strange that there is no mention of the issues with using this with a 5" barrel. But I suspect it is the manufacturer trying to keep the flaws as unspoken as possible. While you can technically put this on a 5" barrel, it will be missing the rear attachment points leaving this unstable and not able to be trusted.
I couldn't even install this accessory as the quality control for this item is clearly a joke. There is a locking collar that you attach to the barrel that is the front support for this extension. One of the screw holes were so poorly drilled that the screw sat at a 45 degree angle and was unable to seat properly. This would have been absolutely obvious to the person making the mistake. They clearly didn't care. And obviously no quality control or they would have seen the jacked up screw hole (it is a very visible defect) I am terribly disappointed and will not be supporting this manufacturer.