Be wary reservations are hard and a bit pretentious! Emailed for a reservation and received a…read more"thanks for your email" but an obvious non-answer, arrived the next day and asked again to be told nothing available or long waits for walk ins. After we shopped at Dior, bought a bag, and asked with shopping bag in hand, the host went to get the manager and we were told we could have a 4pm reservation for set price afternoon tea. If you call/email weeks or months in advance you'll probably have an easier time.
Regardless, I knew it'd be like that and went mostly for the vibe/picture moments I could have. It's 55€/pp for 4 small desserts: a macaron, madeline, chocolate, and rose cream sweet, a drink of choice, and a dessert of choice (cream puffs or raspberry cake). All were great! It's definitely expensive for what it is but if you take into account the experience and ambiance, and you really like Dior, I think it's worth it.