Short answer; book now! You won't find a better place in Tokyo.
I can only echo what others are saying in reviews. Myself and my brother stayed in Yume's apartment just as the world was going on lockdown due to rapidly growing situation around coronavirus. Yume was more than accommodating in making us feel comfortable and was more than happy to help accommodate us if flights were canceled.
This is such a comfortable place in the heart of Tokyo, a secret oasis close to everything. Loved the small touches, 100s of varieties of teas, a fridge full of ice cream, amazing sound system with huge tv. It really does not get better.
If you're on the fence about booking, don't be this is the perfect place to be in any situation!