Recs.
Updated
SpecsUpdate
Pros
Pro Surfaces important information from messages
If an email contains pictures, flight information, reservation at a restaurant, attachments, links, dates, phone numbers and other information that the application recognizes, it will surface that information in its main view. These items can be viewed and interacted with without having to open the message itself. It allows finding and taking action on the important email information quickly.
Pro Intelligent categorization
Inbox tries automatically bundling similar messages together. For example, Inbox will create bundles for travel information, receipts, promotions as well as group messages temporally. It enables also managing these bundles of messages together - they can all be swiped away together.
Cons
Con Not really cross-platform
Only works as an app in Android or IOS, and in browsers.
Con Cannot add multiple labels to an email
Gmail uses labels to categorize emails. Using multiple labels can make it easier to find the email later on. Ex: "work", "friends", "london". Index only allows adding one label per email, effectively turning them into directories. All the benefits of labels are lost, then.