Hi, I seem to remember there being a reason for colletts, but never really liked them, given a choice I will always buy a tool with a chuck; when I'm lost in the middle of a job I can't put up with having to change collett because the bit I want to use is too big or too snall for the one in the tool, always assuming I can find the right size on the bench in what someone described as Clutter's last stand.
With a chuck it's always there on the tool when you need it.
I've always used Minicraft as they offer both chuck or collett and offer a chuck as an extra for tools supplied with colletts.
Dremel tools all seem to come with colletts, but they do offer a chuck as an extra.
A chuck will nornally only grip the tool in 3 places around it's circumference ( or 4 if you are using a 4-jaw chuck ) whereas a collet will provide grip through almost all of the circumference of the tool.
:thumbsup:
As Leo says, a collet will give a better grip, but unfortunately you need one for every size drill bit you want to use. I use a collet on my Archimedes drill as I only use one size of bit.