overall construction. my brother has a full sized aluminum handled M16, and it's rock solid. he's had it for years. he beats the ever-loving crap out of that thing and it never even blinks, which is the reason that i picked mine up in the first place. hell, he used it for a whole season working on a grounds crew for a country club, and nothing will dull a knife up faster than cutting sod with it, yet he did just that. he'd just come home that night, spend a few minutes with a cheap Smith's V-sharpener and it was as good as new.
with the zytel handled smaller ones, the handles and liners are so thin that they flex simply from the pressure of your hand when you're gripping it to press your finger on the flipper, and that flexing makes the screws loosen up and back out. blade play is one thing. handle play is something i've never encountered before or since...
i wouldn't hesitate to pick up another M16, if it was full sized and had metal scales, but you couldn't pay me to trust a zytel model...