[Q] How to root my TWD_MID

Hello all,
I have this Chinese TWD_MID 7" tablet with android 4.0.4 (MID708A13) that I want to root...any help?

The device has "su" file in system/xbin/ ... however it doesn't seem to be rooted as I cannot remount or do any privileged commands.
it keeps saying "Read-only file system"

Specifications:

A13 7inch tablet PC
CPU:A13 Cortex a8 1.2G
Screen:7'' capacitive
OS:Android 4.0

So is there any way I can root this device ?...

Thanks