on a machine we built; I was favorably impressed by the rigidity of the actuator's construction. Still, I question whether it will be rigid enough to cut aluminum at full extension. This also depends on the rest of your machine - it's only going to be as rigid as the weakest component you use. Your dual nut-block configuration should help with rigidity; whether it's enough won't be clear until you try it. But I think it's worth trying it, it's probably not going to work any better if you add slides to the back of it.
I found that with my Z-axis, it helped to add some constant-force springs to keep it from unwinding and dropping when the power's turned off. But maybe your screws are finer-pitched than mine were (1"/rev).]