I find monopods best for square format or rotating back cameras.

I have a Manfrotto monopod with an accessory quick shoe release. It is surprisingly finicky to mount a camera on .

The models that have built in, mini-tripod legs can be handy when there is no wind. They are a decent substitute for something like a camera stand, but they certainly are no substitute for a tripod.

They also can be used as a light stand for a portable flash.

They are relatively expensive.