How do the Ki-Fueled Attack Optional Feature and the Martial Arts Feature differ?

Question

The Martial Arts feature allows for a bonus action unarmed strike after a main attack of an unarmed strike or a monk weapon attack. The Ki Fueled Attack feature allows for either an unarmed strike or a monk weapon attack after spending a ki point (such as on a stunning strike) as part of the action. Am I right in saying that the differences between the two are limited to the following?:

1. Martial arts has to be an attack, Ki Fueled can provide for something else, such as a subclass feature.
2. Martial arts only has an unarmed bonus attack, Ki Fueled attack can be a weapon attack.
3. Both and/or either in any way only allow for 1 additional attack as a bonus action.

Answer 1

The relevant portion of the monk's Martial Arts feature states:

When you use the Attack action with an unarmed strike or a monk weapon on your turn, you can make one unarmed strike as a bonus action.

In contrast, the Ki-Fueled Attack optional class feature for monks states (TCoE, p. 48):

If you spend 1 ki point or more as part of your action on your turn, you can make one attack with an unarmed strike or a monk weapon as a bonus action before the end of the turn.

The main difference is that actions which don't make attacks but do cost ki trigger Ki-Fueled Attack. For instance, if you are a Way of the Four Elements monk and you use your action to cast a spell, you can still make an attack as a bonus action with Ki-Fueled Attack.

Ki-Fueled Attack also allows you to make an attack with a monk weapon (which could be a ranged attack), so a Way of the Kensei monk who spends a ki point as part of their Attack action could make a bonus-action attack with their ranged kensei weapon.

Ki-Fueled Attack was added to allow subclasses to make a bonus-action attack in situations where they didn't qualify for the bonus-action unarmed strike from Martial Arts.

The version in Tasha's Cauldron of Everything also allows monks to upgrade an unarmed strike to a weapon attack, if they qualify for both (unlike the version in UA: Class Feature Variants, which only allowed an unarmed strike).