Yes, it did shoot low, which I took to be due to the fact that extra diameter of the moderator compared to the standard barrel places the bead higher in relation to the muzzle, and thus causes the sight-line to diverge from the bore.
As well as the need to blot out the target with the moderator, I also found the lack of a sighting rib hard to get used to. Adding the low-profile Chinese red dot increased the kill rate because it let me place the centre of the pattern on the target whilst still keeping it in view.
Meanwhile the ATI kit raises the comb, provides adjustable LOP and gives better control under recoil, as well as a better trigger position.
The only problem with it is that it is a bit too light, making the gun more muzzle-heavy than with the standard stock, but I'm thinking of fitting an ATI shell-holder to the butt in the hope that half-a-dozen cartridges will redress the balance a bit.