This is a really simple, medium duty bracket.  It will take a surprisingly large load but it should not be used in any situation where it is holding something UP.   Holding things DOWN, like a table top, is fine.    

In the photograph it is holding (locating) a heavy bench top onto it's base, and has proved reliable in that situation - the full weight of the bench can be lifted using only six brackets, but it never has any impact loads.

They ARE handy for many uses though!

EDIT - I've replaced the bracket pictured with a revised version which can be printed on its side without support to orient the print in an ever so slightly stronger way, but I do hope ultimate strength is not something you are hoping to test on a built piece!