I've had a set of the Tekton double box flex head ratcheting wrenches for a few years now, and I'd describe the quality as very good. They've handled everything I've thrown at them with zero issues.
I've not used the SO version, only handled a friend's, but fit and finish are surprisingly comparable. The biggest difference I see is that the SO is 12-point, and the Tekton is 6-point. This can make the Tekton a little more "fiddly" to get onto a fastener in close quarters; sometimes I have to rotate the ratchet a couple of clicks to enable it to line up with the bolts. If I were wrenching for a living that little bit of time spent might reduce productivity just a tad, and for that reason I can see insisting on the 12-point. Since I'm not in that position, it doesn't bother me.
My only actual complaint is that the joints will occasionally get a touch loose with use and wear, allowing the head move a little more easily than I would like. I just retighten the Torx screw and it's good for another year or so. (Truth be told, I've only had to do that to the 12mm, which is the one I seem to use most.)