What are some opinions? I have one on the way, hopefully.

I like that it can be used on a handgun as well as a rifle. But how does it compare to a DBAL, APTIAL or something similar? Pros and cons...? My research seems to say the IR illumination is better and the IR laser is hopefully equal.

It will most likely go on a pistol, at least to try, assuming I can zero it. If I don't like it on my Glock, I may try it on a carbine or even a shotgun for laughs (nighttime coyote hunting in thick brush, woods).

I run one of these on my primary rifle setup; mainly because the DBAL i2 interferes with my thermal sight picture, so I run the X400v IRC at the 3 oclock position with a surefire pressure switch. I had an issue with the first one I owned, which was one of the 1st gen units, but I sent it back to surefire and they sent me a brand new updated model. Since then it has turned out to be my go-to IR illuminator/laser on my carbine setup. It blows away the illumination on my Dbal single-spectrum and honestly the IR pointer is every bit as powerful as the pointer on the Dbal on High. In my opinion, I like the way the Dbal looks on the front of a rifle at 12 o'clock but after every time I've tried to make it work, I always come back to the x400irc for the simplicity and the IR illumination. I've researched a few threads on here and they flamed the use of the x400 on a rifle pretty good so I kept it with the intentions of selling it and going with the dbal, but honestly, aside from the decent red glow on IR mode, there seems to be minimal downside to it. I rock it with pride now and the DBAL stays in the safe. Good luck!

Thanks.
I'm currently using an OTAL-C and a 600V on my night gun. I wanted something for light handgun use but I keep seeing them on rifles so they must be pretty decent.

They are a decent handgun unit, but it has a pretty high laser offset, and the zeroing isn't the most precise.

The plastic activation tabs on the X-series surefires aren't very rugged either, they should be protected by a holster. I've had them come off several times & get lost even with pistol use.

I run one one a pistol. The laser is as bright as any other civilian unit I've used which is the main reason I got it. The illuminator is great but you're not going to get the distance that you will with some of the other units but it's way more than adequate for a pistol, and adequate for the range of using the laser as an aiming device. If you want to illuminate the far side of a field you're going to be disappointed though. It's powerful but it's more of the flood than a spot compared to others.

The best part is that it seems to hold zero great.

I have a few of them  and compared to the I2 9007, A3 and APTIAL-C the IR illuminator of the X400V wins hands down. As Augee stated there is a faint pinkish glow that can be seen from a close distance/angle from LED based IR illuminators light discipline is always paramount as with any light or even laser based device in a no light scenario. Although the offset is higher if you overlapped your laser with your red dot at the furthest distance you can see "I'll pick 1000 meters for an example" the widest point will never be more than the distance of the center of your bore @ 2 3/4-3" and only gets narrower to the tip of the apex/point where it meets. As far as the laser it's comparable as far as output, but the adjustments are not click adjustable and may walk easier than a click type. Although I never had this problem I haven't tested for a long period of time either. For pistol zeroing you can do it at night and just overlap the laser to the iron sights or it can also be done in a dimly lit room by mounting your pistol to a base, mount a target 25 meters away, turn  on your laser and adjust it to the poi of your iron sights. Your IR laser dot can be seen using most cell phone cameras @ 5-10" away from your target.