The flange is three inches wide.
the ends are sealed, some kind of plug in each end. the screws seem adequate to me, and have tested this by using only 2 screws in one handle and hanging on it, it held - so I installed the other 4 screws.
My grab bars were installed by a local handy-man. He used a special drill bit that would not break the tiles.
I HAD MINE INSTALLED BY A HANDYMAN FRIEND OF MINE HE USED 300LB TOGGLE BOLTS
NOT SURE HAD SOMEONE ELSE INSTALL HE BOUGHT 300 LB TEST TOGGLE BOLTS