I've recently ventured back into the dedicated DAP scenario, and initially got myself the Walkman A55. The last of the A series to sport the Sony linux ROM. And it's a very decent device. Doubles up as a DAC, and bluetooth receiver so my car, which doesn't have an interchangeable radio, nor does it have Bluetooth, is provided the later thanks to this feature on the A55.
And then Mr Walkmans firmware on the device makes it better too, with tweaked sound signatures. Bluetooth is okay, but try to use it with anything like the Sony Linkbuds, and the connection is poor. Battery life is pretty damn good on them.
A100 series however. Whilst they sport Android, and the ability to search your library in the Sony music app, it loses Bluetooth receiver, DAC, playlist mangement, and SensMe channels features among also having poor battery life thanks to Android.
Though, a new A series walkman is on the horizon.