Soft cups and leaking

I am STILL trying to choose between cups (lol). I am leaning toward the si-bell, but I am hesitant, because I don't know if it will leak since it is a soft cup. Does it have enough suction? I am a runner, so I can't use a cup that will leak at all... My other option is the fleurcup, but I like that the si-bell is a nice, soft cup that has capacity.