I have had both kites 9 and 12m in Bandit Dos and 7 and 10.5m in GT.
Currently I am on the Core Combat GT.
Both kites fly really well, turning is really quick and both are very grunty.
I kind of like the on off power of GT, seems easier to control than the steam train feel of the Dos.
My issues with the Bandit Dos was really related to setup and depower.
Due to the requirement of pumping each strut up to a very high pressure 10PSI on LE and 12PSI on each strut, compared to 6.5PSI for whole kite through simple one pump solution. Now it might not be an issue for some, but I simply would not buy a kite with no one pump again. Let alone requiring extreme pressure.

As previously mentioned the Dos does not depower as much as the GT, this tends to be an issue especially with larger sizes as wind picks up, although you have the option of landing the kite and readjusting middle line knot.
Construction wise both are super good.
Wind range of both models is awesome 7m GT goes from 16knots on surfboard all the way up. 9M dos has similar bottom end to 12m bow kite and probably can hold up to 25knots with right depower setting.
To me the GT bar rules it is simple, has pull pull depower vs rope cleat which takes more getting used to and will wear quicker.
I prefer the push away system on the GT to the old style velcro one on the Fone.
But don't listen to anyone else try both kites yourself, and if you are getting a quiver 2 of these delta kites will cover most of the wind range.