Very interesting looking product. If it's readily available and reasonably priced, and commonly accepted by your building officials, I'd say go for it! BTW, what are coach screws? That's not a yankee term at all that I know of. If you install the channels within a very few days of the pour you'll even have a easy time drilling the holes for the screws.
I think, considering the labor involved in cutting the foam before or after, and the work to cover the gap if you cut before the pour, you'd be better off to cut the foam after the pour. One factor to consider though, is what kind and amount of nubbins, if any, are on the concrete surface caused by depressions designed into the interior surface of the foam blocks, particularly at the joints. The time spent in knocking them off to give a smooth surface for the channel might be better spent in cutting the foam before the pour. My only concern is the potential weakness you create in the wall of blocks that you have to compensate for with whatever you use to cover the gap.
As always, there is no one single correct answer. There is only the best answer for one's specific circumstances!
And the responsibility to determine that rests on your shoulders. Hopefully, the comments offered here provide good guidance to help you out.