The Eclipse Red ring is amongst the most well known Adjustable razors.
James Neill & Co of Sheffield, England owned the Eclipse brand.

Red Rings were manufactured at a time when blades were thicker and had more spring in them. Using the current thin DE Blades I would not really consider them to be adjustable.
There is a magnet in the underside of the twist-knob to facilitate the picking up blades off a flat surface, which is probably their most well known feature.

My understanding is that there are 5 different generations: (Dates are approximate)

Gen 1: 1933 - Silver Plated 3 Piece with embossed logo on the top cap and no painted Red Ring.
Gen 2: 1934 to 1936 - Silver plated handle, Chrome Head 3 Piece with Embossed logo and no painted Red Ring.
Gen 3: 1936 to about 1939 - Chrome Plated Two Piece. The twist knob was pinned into the handle, there was an embossed logo on the top cap and the ring had Red Paint.
Gen 4: 1939 to 1940 - Chrome Plated Two Piece (pinned twist knob) and no Embossed Logo. The ring was painted Red
Gen 5: 1940 - Chrome Plated Two Piece and no Embossed Logo. Only Eclipse engraved on the handle and the ring wasn't painted Red

Within each of the generations there were 5 different models. The razors themselves remained the same but the cases supplied were different:
Model W - Blue Leather pouch (1 blade included)
Model MM - Mottled Green case (1 blade included)
Model BB - Mahogany colored bakelite case (3 blades included)
Model HH - Ivory and Black bakelite case (5 blades included)
Deluxe - Chromium plated case (10 blades included)

They are considered an Open Comb with a bar on the underside of the teeth. The bar is really there just to hold the teeth in place. I would say that they are more of an Open Comb / Solid Bar Hybrid. They all have the round posts on the base plate that protrude through the top cap.
All have the magnet® in the bottom of the twist knob, which is probably their most famous feature.
Another is the words Eclipse engraved into the handle. It seems that towards the end of their run they no longer engraved Red Ring on the handle.

There are two patents applicable on the razor. In date order they are:
The first is GB344280 which is applicable to the magnet. The number is stamped into the brass around the magnet. It is dated March 5, 1931.
The second is GB3809570 which is applicable to the razor itself and that number is stamped on the underside of the head. It's date of acceptance was Sept.29, 1932.
If we look at the last two pages of the later patent document, there are three different versions, two of which have a spring mechanism that push the blade postsup against the top cap. As far as I'm aware neither of these designs ever came to fruition.

Eclipse Red Ring Gen1	Eclipse Red Ring Gen2	Eclipse Red Ring Gen3	Eclipse Red Ring Gen4	Eclipse Red Ring Gen5

The Difference between the twist knobs. Generation 2 vs Generation 3. I found a Red Ring that had everything that would make it a Gen-2. It was a three piece and had the chrome top cap, so I bought it When I received it, I realised that it was actually a Gen-3 but the twist knob was no longer crimped into the handle. Since then I've seen a number of them. Here's how to tell the difference: The twist knob on the left is from a Gen-1 and the one on the right is from the Gen-3. If you look at the area that is pointed out, on the Gen-1 it is slightly raised while on the Gen-3 it is slightly recessed so that it can be crimped. (clicking on the image will open it in a larger new window)

These are the instructions that came with the razor.