I found this article (and the
other related one) a bit confusing because they seem to conflate Nvidia Reflex (NR) and Nvidia Reflex Latency Analzyer (NRLA) and use the terms interchangeably.
NR reduces latency. It is comprised of the NR SDK (which includes a Low Latency Boost feature) which game devs can use, and an Ultra Low Latency Mode in the driver. It does not require a special mouse or monitor. You need a 900 series or newer GPU to take advantage of NR SDK (Boost feature works on any GPU though).
NRLA does not reduce latency, it merely measures latency. It requires a special mouse + monitor. Not seeing anything about GPU requirements.