Its like razor's.the eight blade gillette superglide with the free one blade detail razor. It's a con your grandad got a better shave with a cut throat razor. No doubt that a carbon steel trowel is a trowel that gets the job done start to finish. Free choice though so do as you will.
Trowel it when it's ready. Lol all depends, doff backgrounds, higher suction etc etc. I like to trowel it on the earlier side, so don't need to grind the f**k out it, others don't care about a grinding match, I just like it easier on myself lol