Apologize to the poster for derailing your thread. You probably don't know me but derailing threads was my specialty back in the day here.
As stated, the corner trowel is great for setting tape. However it's a pain to hold on to and set down anywhere due to the shape.
There are generally two sizes also. The smaller size is great for getting in the 3 ways but the larger variety is better for feathering out the majority of the runs IMO.
When you start talking about finishing with one is a different story. By design the tool will take off too much in the corner the more you press in while adding more just outside the tape edge giving a finished inside corner that resembles the middle of a open book...... kinda. :blink:
Anyways, I always had a couple when I finished by hand for setting tape before corner rollers and angle boxes.
Just my .02.