I know that they are owned by Honeywell, but what exactly is the point of having 3 sub-companies for essentially the same product with a different name?
They were all established brands acquired by a single conglomerate probably, they just want the existing name recognition.
They’re also 3 products aimed at 3 completely different market segments. Notifier is for small to medium sized applications with some level of complexity, fire-lite is dirt cheap off the shelf systems for small buildings, like an Applebees or something, and silent knight is more well known for being a dialers or used for sprinkler monitoring panels. Never a good idea to mix your super cheap brand (fire-lite) with something more professional (Notifier).
Thanks for the reply! I had no idea they were meant for different settings, good to have some more knowledge about those brands 
Fun fact: A few years ago I had the opportunity to visit their facility in North Branford, CT. All four companies have their own business space, but share the same factory. That’s how similar their products are!
(The alarms in the building were mainly System Sensor MASSes, by the way. How shocking.)
There’s actually a fourth brand you didn’t mention – that’s Gamewell-FCI.
My theory of how this group of companies is organized is like this.
System Sensor provides addressable devices, detectors, modules, and components for the other four brands…
Notifier is at the top, because they get most of the new technology first (with the exception of the GWFCI S3)
Gamewell-FCI is next, they get what trickles down from Notifier.
Silent Knight is next, they develop unique systems that are inexpensive and easy to use.
Fire-Lite is last, who is the cheapest but also serves to fill the “holes” in the product lines of the other three brands – primarily conventional with the MS-2, MS-4, MS-5UD, MS-10UD.
Somewhere in this list is Honeywell Life Safety, a corporate brand sort of similar to Simplex that uses modified Notifier products. Their purpose is to engineer, install, and service surviving Honeywell DeltaNet systems and also to handle HUGE fire systems in high rises or very large complexes (such as Massachusetts General Hospital in Boston, MA).
Did not realize Gamewell-FCI was part of Honeywell. Is this the same sort of idea with Siemens and Cerberus-pyrotronics?
No, Siemens bought Cerberus-Pyrotronics and re-branded it to Siemens. The Cerberus-Pytronics products continued on but the name died. The Gamewell-FCI name and brand still exists.