I have a 595. With that said the 396 saves you money by getting your music from your phone via Bluetooth only. Same for nav. No audio cable from what I gather.
For me I like having the music on board the gps unit. With the option to go to my phone (595 Zumo). Everyone is different. The only other thing I have heard is it is slower to boot. I am not getting any younger Oldguy I don’t like waiting.
The 2 pin I am referring to is the electric contacts. The cradle itself has large slots and sturdy latch to hold the GPS, no issues even when bouncing around on dirt roads. There is no lock on the latch tho. And the 3xx series GPS is much lighter than the 5xx.