I like/use the plastic locking clip kind as well, for the same reasons other's mentioned. Only thing I would add is that many plastics can degrade with long term exposure to direct sun , so I would check throughly before each outing.

I also believe in putting the clip in both lips, unless your going to stop and fillet your catch as soon as you get a meal. Hauling a large fish or stringer of fish with mouth(s) open for any distance is like dragging an anchor.

I also believe as KF says, the stress it puts on a fish isn't helping any in the flavor dept, much as venison from a wounded animal being chased and then dispatched is different from one the adrenaline hasn't been running thru.

KF's cooling tip is what I use. I went to my bank and got a canvas coin sack. On a 90+ day, I hauled a beheaded/gutted LT from Jean Creek to end of Sturgeon lk. I just kept the bag wet and under my seat out of the direct sunlight. Works great as an overnight cooler hung well in camp.

Jimbo, after seeing that  infamous picture of your fingerling catch ;), you could probably get by with a quart zip-lock for a fish locker eh?