Still using a N900 as my primary, though at this point it is less smart as web2.0 forward has ruined the usefullness of too many devices in exchange for tracking users across websites amd I guess some mobile customizations.
I have to bring a LineageOS w/microG device slaved to my N900(bluetooth tethering) to use NFC transit card and browse transit websites as well as managing my Pebble watch though I get full use function of the Pebble on the N900 with Maebble.
Until yesterday I had a working tablet-ized S4 mini, a nice pocket sized slave device, but botched the LCD connector when replacing the auto-firing home button. Tablet-ized as I disconnected the telephony antenna connector and ran
to disable attempts to use the cellular radio, sadly this also leaves the GPS unpowered but the N900 has nav and I can transfer the stationary coordinates to the fakeGPS app if I need it on the Samsung, I might even have figured out a bluetooth-serial bridge and script had I not damaged that device and needed that function.
I will probably go back to my (Kingston early emmc death now repaired) larger Nexus7 (flo) as my slave device though I miss having a pocket sized tablet with removable battery and SD card.
The one downside to a tablet-ized and LineageOS w/microG S4 mini is that it requires at a hardware level external power or a modified pin connector to do USB OTG.