What makes FIRECLEAN better than SLIP 2000. I currently use SLIP 2000.

Why is it so praised? And not "It works for me". I understand both are water based, but what actually makes
FIRECLEAN better than any other lube right now? Is there something chemically that's superior? I don't understand
the hype.

I'm currently using Fireclean with a 1911, several revolvers, and an AR for about a year now.  I started using it to make cleaning revolvers easier and that has generally been the case versus Breakfree CLP, but not materially so.  It's a wash for the 1911, and the stuff doesn't feel to be as slick as other oils (e.g. M-Pro7) on the 1911 and AR.  The AR clean up is easier with Fireclean on the typically dirty stuff versus M-Pro7.  My observations aren't scientific by any means, but I've migrated to using Fireclean where things get dirty and use other stuff where friction is the primary concern.

As a very unscientific control, I'm also using Tetra gun grease on the bolt/carrier of a 7.62x39 AR which sees some nasty ammo through it on occasion.   Though this AR looks dirtier than the Fireclean AR, it cycles just fine, needs a bit more time to clean, and holds the lube a lot longer than the Fireclean AR.  YMMV.

For those using fireclean, are you also cleaning your barrels with it?

We do not clean barrels with it, every other part of the firearm we do.

If you don't mind sharing, what's the reasoning behind that? I am currently leaning towards doing the same once by bottle arrives.

The barrel is the key part of any rifle, and its difficult to remove all the fouling tucked in or around the rifling. If you utilize fireclean in the barrel and you miss a small amount the residual carbon will attract more.

Aside from that, FL and FC failed a salt corrosion test, will our firearms ever be subject to that? Possibly in our field, but not for the recreational shooter, we utilize MPro Bore Gel for that reason