On paper this thing makes a pretty nifty all-in-one package (minus a visible laser) for rifles. Especially if you add the long gun kit. Yet I don’t hear anybody talk about them very often. Is it that much inferior to stuff units like the various lower end DBALs or OTALs that are usually paired with a weapon light?

I've mounted one to a M4gery it worked ok, but the lack of positive clicks for the adjustments and zero retention made me opt for a true rifle LAM. I do have one mounted on my backpack/camping rig a Ruger PC carbine with a Aimpoint Comp M4 and for what it is it should do fine.

IIRC there was some discussion about the distance from the bore would magnify a converging/diverging zero at rifle distances.  If that appeared to be posing a problem you could try an offset zero.

I have the Surefire X400V kit you mention. It's an excellent quality unit but I use it only on my Glock. Mounting on a rifle may be tricky. Maybe on the top rail where a front BUIS would go. The IR laser will be quite off from the bore and the IR laser hanging out on the far end of the rifle will get banged around and I think it's too delicate for that. One good hit on the little lever that you select light, laser, both will probably break off.

I use an OTAL-C on my night rifle along with a Surefire 600V or V1 light.

I love my Surefire X400V IRC light/ laser combo's. I have 3 of them and need 4 more. I don't think it would be a good match on a rifle due to the controls and type of light that it is.