Looking at the site you’ve linked to, he pretty much admits that the problems are down to poor workmanship and poor tools. The photo shows a seam that will not only leak but quite possibly tear apart under serious stress. The situation is much the same as with anything else you might make, be it tent, shed or packraft: you need to have the right tools for the job, to develop the skills to use those tools effectively, and have a system to monitor your own skills. Have all that in place and whatever you make will last you as long as anything from the big names. Possibly longer in many cases.