I have the full sized Kershaw Cyclone AND I have stubby thumbs...there's no way it would ever open one handed without the assist. I also have a Gerber EZ-Out (my former pocket knife). I'm not sure how they get off calling that a one handed opening knife but the Kershaw was a Godsend when I discovered it.

If the safety on the Leek you mention is the same as mine Mike, it's not a safety, it's a switch that allows you to turn the assist off...basically just disengages the torsion spring.

Also, you need to have the blade pretty far open before it 'assists' and the spring holds the blade closed when it's closed past the assist point. I've been carrying mine nearly every day since October and it's never felt anything but safe. The lugs aren't sharp and don't catch on stuff...same with the index trigger (my preferred method).