So unlike martial arts where you take the Attack action and make 1 attack (2 at level 5) and can either make an unarmed strike as a bonus action or 2 unarmed attacks by spending a Ki point on flurry of blows RSB only allows you to make two RSBs as a bonus action by spending a Ki point if you take the Attack action and at least one of the attacks is a RSB.
So you are correct that you can RSB 4 times at 5th level (2 as part of the Attack action and 2 as a bonus action for 1 Ki point) but although similar to FoB it isn’t FoB
edit: in previous posts I’ve stated that it’s like FoB (getting two attacks as a BA for 1 Ki, but using RSB instead of unarmed strikes) but it is it’s own special attack. Sorry if any of my responses added to confusion.
So unlike martial arts where you take the Attack action and make 1 attack (2 at level 5) and can either make an unarmed strike as a bonus action or 2 unarmed attacks by spending a Ki point on flurry of blows RSB only allows you to make two RSBs as a bonus action by spending a Ki point if you take the Attack action and at least one of the attacks is a RSB.
So you are correct that you can RSB 4 times at 5th level (2 as part of the Attack action and 2 as a bonus action for 1 Ki point) but although similar to FoB it isn’t FoB
edit: in previous posts I’ve stated that it’s like FoB (getting two attacks as a BA for 1 Ki, but using RSB instead of unarmed strikes) but it is it’s own special attack. Sorry if any of my responses added to confusion.