Half the problem is that a full-sized chain is more often than not closer to warmblood or even draft! Monty is about cob sized around that part of his muzzle, he takes a cob sized flash strap. I don't want to cut it though because I may end up with a horse in the future that needs the full length of the chain.
My main problem is the chain guard, I've ridden in that bit several times and never been picked up by a gear checker for the chain being so long I have to put the ends together with a velcro loop to keep it from smacking him in the face. They just don't like chains being totally unprotected because they can pinch or rub some horses, and so of course I got a chain guard only to find out that it's too big for my horse. I do know one person who uses vetwrap as a chain guard and has never been gearchecked out because of it.
The OP asked if the kimblewick is a harsh bit, which I didn't realise when I first posted. I'll answer that question now. It depends on whether or not you use the slots, and which one you use if you do - no slots and it's basically a hanging cheek snaffle with a chain. Top slot has minimal leverage even if you ride with your hands very high, bottom slot has a lot of leverage. The kimblewick can be anywhere from the softest curb bit out there, to fairly harsh, depending on the configuration it's used in. Not as strong as a pelham, but not to be used by anyone with bad hands in its harshest configuration.
There are about 4 people at my pony club who I have seen riding in a kimblewick. The rest ride in snaffles, gags or pelhams. But kimblewicks are great bits if you need just that little bit more than a snaffle, and don't want to go to a harsher mouthpiece.