I stayed at Chapter Spitalfields for one month in July, as I was on a research stay. Let me highlight some of the best things about Chapter. The location is great, the apartment is great and the common areas are wonderful - especially the in-house Starbucks and gym. I really enjoyed those. It is super quiet and safe, and the staff are all welcoming and kind. When I experienced a faulty shower, it was fixed within a day.
However, at the same time, this is student housing, so there are some things that you have to accept, if you stay here. The students living in the building have different standards in terms of cleaning up after themselves, so the level of cleanliness is not always high. But again let me stress that they are quiet and well-behaved. No remarks there. Additionally, it gets quite hot in the apartment, so remember to pull down the curtains.
All in all, a fine experience - I would stay with Chapter again, if I find myself in London for a longer period of time.