Hi, I'm the developer of Doze and ShutApp. Thank you all for discussing Doze here and I want to say something:
1. For unrooted devices, VPN is the only way to block data. So this is one of those things we (or any others) have no alternative. The VPN is a block for data flow and the data will not be sent to any server.
2. In Marshmallow's Doze mode, network access is blocked; wake lock is ignored; alarms are suspended. While our Doze just blocks data flow.
In most cases, however, apps cannot do anything without network connection. We can reach the same result in both ways.
3. Why we developed Doze app even though all of us know Android 6 has the new feature?
Marshmallow's Doze is a very nice feature but it's too hard to get into the mode. Imagine a day I'm hanging out and I'm walking all the way, I can't get into Google's Doze then. In my point of view, that's one of the cases that we need battery lasting as long as possible. That's why we develop Doze that needs to set up VPN and develop other features like active list, aggressive mode, Charge/Wi-Fi preferred mode...
20% of our user base for Doze app are Android 6.0 users. For them, our Doze app may be a better option as you can get into Doze at anytime you want.
4. Great to see that we have similar apps like dozzzer app, with whom we share the same purpose - battery saving. Battery performance is always a problem for Android system, and we hope that Google can do something and make a world without battery saving apps.