Crawford's ruling on Shield Master was that as long as you are going to take the Attack action on your turn, the bonus action can be used before or after the Attack action is actually taken.
The wording of Blade Flourish is the same as Shield Master, meaning, if I'm to understand this correctly, that if your intention is to take the Attack action, then you get the bonus to your movement before actually making any attacks.
And another question. I just realised that if you use two-weapon fighting, you might not qualify for using any of your Blade Flourish options on the bonus attack.
"...if a weapon attack that you make as part of this action..."
Blade Flourish options only qualify if they're done on an attack as part of the Attack action. The bonus action attack for two weapon fighting comes as a consequence of using the Attack action, it is possibly therefore not part of the Attack action though.
And another question. I just realised that if you use two-weapon fighting, you might not qualify for using any of your Blade Flourish options on the bonus attack.
"...if a weapon attack that you make as part of this action..."
Blade Flourish options only qualify if they're done on an attack as part of the Attack action. The bonus action attack for two weapon fighting comes as a consequence of using the Attack action, it is possibly therefore not part of the Attack action though.
If i am not mistaken there was something similar to this in sage's advice and it clearly stated that if it asks for attack action instead of just attack (for example melee weapon attack) than bonus action attack does not trigger the ability.
The wordings between Shield Master and Blade Flourish have an important distinction, in my opinion.
Shield Master's wording includes an "if": "If you take the Attack action on your turn, you can...". That condition can be argued to count as intent, and I'd imagine the DM will require a full statement of intended actions, including that Attack action (for example: "I shove him to the wall with my shield, follow 5ft, and attack him") just to make sure there aren't any paradoxes (such as a Reaction that moves him out of your attack range, thus cancelling your Attack that gave you the bonus action - I'd rule the attack wasted, rather than allow a change of action).
Blade Flourish, on the other hand, mentions "whenever". As in, when you make an attack, you get the bonus speed. There's no intention in that condition, it's all about a trigger.
To make matters worse, the the rest of the bonus, the Flourish itself, is triggered when your weapon attack actually hits your target. You can't make a flourish assuming you will hit with the attack later - there's no guarantee you will.
The second question is more straightforward, but I'd be more lax.
Contrary to Extra Attack, that gives you more attacks as part of the Attack Action, the two-weapon fighting trait allows you to take a bonus action for an additional attack when you take the Attack Action. It's triggered by the attack action, but not part of it.
Still, I'd personally allow Blade Flourish to trigger from an off-hand attack; doesn't seem to break anything by doubling your chances of success any more than Sneak Attack does for a dual wielding rogue - although only one 10ft speed increase per turn; you still only take the Attack action once. :p
Crawford's ruling on Shield Master was that as long as you are going to take the Attack action on your turn, the bonus action can be used before or after the Attack action is actually taken.
The wording of Blade Flourish is the same as Shield Master, meaning, if I'm to understand this correctly, that if your intention is to take the Attack action, then you get the bonus to your movement before actually making any attacks.
And another question. I just realised that if you use two-weapon fighting, you might not qualify for using any of your Blade Flourish options on the bonus attack.
"...if a weapon attack that you make as part of this action..."
Blade Flourish options only qualify if they're done on an attack as part of the Attack action. The bonus action attack for two weapon fighting comes as a consequence of using the Attack action, it is possibly therefore not part of the Attack action though.
The wordings between Shield Master and Blade Flourish have an important distinction, in my opinion.
Shield Master's wording includes an "if": "If you take the Attack action on your turn, you can...". That condition can be argued to count as intent, and I'd imagine the DM will require a full statement of intended actions, including that Attack action (for example: "I shove him to the wall with my shield, follow 5ft, and attack him") just to make sure there aren't any paradoxes (such as a Reaction that moves him out of your attack range, thus cancelling your Attack that gave you the bonus action - I'd rule the attack wasted, rather than allow a change of action).
Blade Flourish, on the other hand, mentions "whenever". As in, when you make an attack, you get the bonus speed. There's no intention in that condition, it's all about a trigger.
To make matters worse, the the rest of the bonus, the Flourish itself, is triggered when your weapon attack actually hits your target. You can't make a flourish assuming you will hit with the attack later - there's no guarantee you will.
The second question is more straightforward, but I'd be more lax.
Contrary to Extra Attack, that gives you more attacks as part of the Attack Action, the two-weapon fighting trait allows you to take a bonus action for an additional attack when you take the Attack Action. It's triggered by the attack action, but not part of it.
Still, I'd personally allow Blade Flourish to trigger from an off-hand attack; doesn't seem to break anything by doubling your chances of success any more than Sneak Attack does for a dual wielding rogue - although only one 10ft speed increase per turn; you still only take the Attack action once. :p