I've used that very tool with great success, maybe you had a duff one
thats what i thought and they replaced it for me
on previous experience when i done the series thought i was doing something wrong
spent hours making sure everything was just right, even bought another roll of copper
everytime i tightened them up the flare just split, i tried different tightnesses and yet still split
so after the flare burst i got a specialist in as i was to scared to use the car and the thought of not having any brakes and possibly hurting someone scared me to much
just couldnt understand why i couldnt get good flares as the tool had good reviews
but maybe it was a bad batch , never did get to the bottom of it , wasnt the copper or fittings as the other guy flared the existing copper and was fine