Since nobody responded to your post, I'll give it a try.
First, I started detecting as a youngster using the old BFO detectors before discrimination circuits were incorporated in detectors. I wasn't actively detecting when discriminating ability was added to detectors. I got back into detecting around 2008, so I missed the active days of the two filter discriminators which came about in the early 1980's I believe. It's an analog system, which at the time allowed users to slow their swing speed to achieve maximum depth over the prior four filter system which required a fast swing speed to get maximum depth. It provided good user feel/feedback, it is said. I have never personally used a two filter machine. The two filter system didn't have a visual target ID.
What the F75 does, to the best of my knowledge, is combine the older two filter analog discriminator with a computer processor based sampling process. It allows for a faster swing speed to achieve maximum depth, while still getting extremely fast reset times where multiple targets exist. That gives very good target separation in trashy areas. It also obviously has a visual target ID display which the old analog two filter discriminators didn't have,
A unique feature is that it's tone ID is separate from it's visual ID. The immediate,tone ID in some processes doesn't always match the visual ID. As it is described in the manual, "The audio is optimized for quick response and target feel, whereas the visual system provides the best numeric resolution of Target-ID."