I will list them, and I know that you mentioned quite a few.

1. Being able to use what you have
2. Lower startup current
3. Ability to add extra capacitors at the same time as switching in
the other motor, for perfectly balanced third phase

My phase converter is one of relatively few homemade things that I am
actually very happy with and that does not give me any trouble.

I also have a dual motor unit. 10 and 15 in my case. I'll just emphasize
that you need to delay the starting of motor 2 by several seconds. Spreads
start load.

Karl