They do break - of course they do, but with a little practice you really get to instinctively know their strengths.
Presonally, I love the little beggars. If used at the right time in the right situation they can get amazing reactions, but as zig-zag says - read the other thread

as for me the ST.El.Th jig is in the long run by far the cheapest way to go.
If nothing else it means you can practice til your hearts content.