I have owned many carbines in my life and built a few myself, but my weapons built by MSTN are by far the slickest, fastest, and most reliable tools that I have. That is probably why I have gotten rid of the rest of my carbines for the two built by MSTN.
MSTNs attention to detail goes far beyond the norm. I have rarely had a weapon run as dead-ass reliably out of the box as I have my two from MSTN. The customer service and communications are outstanding. Their custom builds are constructed of the finest materials to exacting standards by a trained Mechanical Engineer who is only slightly less particular than I am! I would not know about their warranty service, as I have NEVER HAD A WARRANTY CLAIM on any of their products, but I strongly suspect that their warranty is as strong as their products.
I would never go anywhere other than to MSTN for anything that they sell and I would never buy a carbine from anyone else.