I don't have any direct experience of this model but with twin screws and a single rudder I would think that the model would certainly benefit from some help from the propellers to improve its handling characteristics.
You can do this either by using a mixer which slows down/reverses the inboard prop on a turn or by having independent motor control commonly referred to a 'tank steering'.
Tank steering is good for slow manoeuvring such as when docking but less suitable for steering a straight course on the water unless you can lock the two sticks either electronically or mechanically. Personally I would say that a mixer is the best bet. Action R/C Electronics do a combined twin controller and mixer P94 **LINK** which would probably be the most appropriate.
If you really want to keep the cost down with a single speed controller connected to both motors then it is possible to fit a limit switch on the tiller which cuts the supply to the inboard motor at a desired angle of helm. (It is actually possible to reverse the inboard motor but the wiring becomes a bit complicated at this point! – easier to get a mixer!).
Colin