I have been behind plastic trowels from the year dot, and you can read about all my experiences with them on here and also on The Plasterers Forum. I have always liked how they troweled up multi finish and how easy it was on your joints as you don’t need to apply the pressure like you would with your standard trowel.
I have one of the same but never got on with it. I also have the ox plastic trowels they are good easier on the joints, what I found though is they dont close the the finish in enough as a metal trowel does so if u look down the wall you will see it is all still grainy. They are the b*ll***s for bringing water out and cutting time.