I seem to be removing my props often, and I worry that my hand holding the motor while I torque the collett on or off is not strong enough and I certainly don't want to use a steel tool like a Channel Lock. So, I use a small plumbers strap wrench, pictured below.
This one is overkill because it is made for, well, plumbing. Specifically for attaching chrome or polished stainless fixtures to pipe stubs without scratching them. You can find cheaper, smaller and better strap wrenches at Grainger or Home Depot. In fact, the cheaper the better - you shouldn't have to pay more than $10 for an adequate one. The benefit of a strap wrench is that it applies pressure evenly all the way around the motor.