The first thing to notice about Onavo is its awesome icon. Totally random, yet in my opinion very cool and nice looking. But that's irrelevant, so onto what the app actually does. Once installed on your device, Onavo prompts you to install a new "profile" onto your phone. Once this is done, all of the data you use on your phone over a mobile internet connection (not WiFi) is routed through Onavos servers and compressed. This has two big benefits. Firstly, it means that the speed of your data connection should improve substantially and secondly each thing requiring data that you do on your phone will use less data than before. This means you will be able to use more of the data features on your phone that you would be able to without the app, without going over your monthly limit. This could also be very useful when abroad, where some carriers charge you per megabyte used. Using this app would use less megabytes and result in smaller charges.
A nice feature of the app is that you install it, set it up and forgot about it and it just works. Setting up is easy, you just need to install the profile when prompted and hit the "turn savings on" button. Once this is done, even when the app is quit all of your data will still go through Onavos servers and be compressed.
The app also offers a statistics section, which is great if you enjoy looking at statistics or would like to know where most of your data allowance is going. It also lets you know how much less data you have used by using the app than you would have used if you had not.
Unfortunately the app does not compress YouTube videos or other live streams though the developers say that they are working on this and it may be provided in a future update.
The app is totally free, so probably worth a shot even if you think you don't need its awesome features.
Had a go with this app? Let me know in the comments below!