A plastic trowel ive played around with is the Refina plaziflex. Much more lightweight and glides across easier - I even tried it to apply plaster and the results were great, but not what it was intended for i dont think.
They don't need much water, if any, when your troweling and designed more to be much easier on the wrists even more so with the sponge backing as you don't need to apply as much pressure