Its important, you don't want it firing to the wrong post and arcing wears out the terminals fast especially with high energy ignition. However you should be able to adjust it if the box allows the reference angle to be changed, worst case scenario you could alter the distributor to physically alter the angle. The rotor tip needs to be wider than with a mechanical advance mechanism, and obviously should remain in contact with the correct terminal throughout the timing range - e.g. if the base angle is 10 degrees BTDC and the max is 30 then you need a tip that is 20 degrees wide and should be centred on the terminal at 20 BTDC.
Multiple coils and direct ignition offers its own advantages but the cost of the coils alone can add up and plenty of factory EFI systems use distributors with no issues. If this system is reliable then the fully programmable timing alone is definitely worth having.
Heath's right, it's not normally a big deal, especially with only six cylinders and even less so with a big Delco style cap. But I'd certainly be careful with a V8 that uses a small, non-HEI style cap. Even without any external timing jiggery they can be prone to arcing in the cap.
And remember that dissie rotation is half that of the crank, so 20 degrees of externally supplied advance (and this includes vac adv) puts the rotor only 10 degrees out of alignment. Still, it's something to keep in mind.
If easy tuning is the objective and you have to or want to keep the dissy then I think a Delco is the cheapest and simplest option. You can even use them with a CD box like an MSD but it won't make it any faster.