It might be cool now, but it's still not safe to put above your head in a rollcage. The tube next to the weld will tear away instead of deform like a bent tube would. I've also seen a few trucks with cracks from excessive nerfing or just plain fatigue where the stress riser miter cap is placed. A bent tube is not as strong as a straight tube, but much stronger than a miter joint.
Depends on where you put them. If it's the top of the A pillar and you tie your windshield bar and roof X brace in so that it covers the miter, it will be fine. Then if your running a vertical window bar with it tied in on the bottom side of the joint, shit ain't going no where.
I recently ran into this question when NASA said my cage would be illegal. They state the tubes must be one piece with bends and NO sleeves/miters. But even from a distance you can see almost no TT's are built this way. It truly depends on who is doing the tech and what exactly the rules say. But like barge says if multiple tubes land in one spot and support each other it will hold up