I do not believe it is a strong because there is so much tension on the needle thread that it does not stretch as much. That makes it more likely to pop under stress. If I were doing the raglan tee, I would probably serge the seam and then do a decorative flatlock over it (by disengaging the knife and flatlocking over a fold of fabric). Mel has a good tutorial in the downloads (I think the techniques section) that shows flatlocking on underwear and a few different options.