I have both the Deepoon E3 (which as an OLED 1440p panel just like the B1) and I have a Pimax 4k with serial 100 (so with a true 4k LCD panel)
Advantages of the E3: better colours, more contrast, more brightness, more 'steady' image (the Pimax 4k is a bit 'wobbly'). When I look for example at the 'dome' from SteamVR and when I move my head, the image stays really steady. It's like I look into a room. But with the Pimax 4k the dome lines wobbles a bit when I move my head. That's because of the (much) higher response times from LCD.
Advantage of the Pimax 4k: SDE !! There's virtually none. Image fidelity is higher, the image is much sharper and therefore feels more realistic to me.
I personally prefer the Pimax 4k LCD, but I certainly can see why others would prefer an OLED 1440p panel.
Both of the panels come with their own disadvantages and it's really a personal preference. It's almost like asking a person, what do you prefer, to live without legs or live without arms ? Tough call !