They're phenomenal.
Recently, the green laser on my SIRT Pro started shooting far to the right. No amount of adjusting the screws was effective at bringing the POI back to the POA. Upon disassembly, a small piece of plastic fell out of the laser module, which was evidently the piece of material that sits against the rear of the laser, allowing windage to be adjusted. After a botched attempt to glue it back into place, I contacted NLT to ask if they sold replacement parts.
I spoke with Jen Goodin, their customer service lead, and she recommended just sending it back to the factory for repair. I was a little dubious, as the pistol was long since out of warranty (it was purchased in 2011), more than a little beaten up and butchered by my attempted surgery. I shelled out the $20 and shipped it to them regardless.
One day after receiving the package, the pistol was on its way home via UPS. The module was replaced and POI adjusted free of charge.
So, I wanted to take a quick moment and share my nice experience with them. In the unlikely event you don't already own a SIRT Pistol, you should buy one immediately. Invaluable training tool.