It stops you from smearing your eyepiece, soaks up sweat from your brow, makes the eyepiece a little more rigid for those shots when you end up using your head as a stabilizer, and color-codes the cameras! I am forever hooked on these!

I called it an accessory, but it's more of a must have for your viewfinder. Great for stopping light leaking into it and very comfortable

This makes my Z finder much more comfortable when using it for long periods of time. Getting it on the Z finder was a bit of a struggle at first, but once it's on it's great. I'd consider this a necessary accessory for the Z finder. I just wish I knew about it sooner.

I prefer the micro fiber over the chamois. It's cleaner, more comfortable and very easy to work with. We shot on a 104 degree day and having this eye cushion was a blessing for the DIT and DOP.

I bought two of these for my Panasonic HMC80 and AF100 cameras. They fit snugly over the stock rubber eyecup -- wasn't sure they were going to be big enough at first, but after a little massaging they went on fine. They are very comfortable and allow a better seal between my eye and the viewfinder, reducing extraneous light. The surface is also very comfortable when using the camera for hours at a time, and the red color attracts some positive attention! I actually wanted something bright to remind me to cover the viewfinders when not in use to prevent sun burns on the LCDs -- I've been bitten by this once. Now I'm looking for an easy to use soft cover to go over the eyecup that can be put on and taken off easily, and won't get lost all the time. My only concern is how durable these will be over time, but it's not a big problem because they're cheap and easy to replace when they wear out.

Comments about Blue Star 90132 Red Microfiber Oval Large Eye Cushion: I attached this to my ZACUTO EVF FLIP pro. Without this cushion I was rubbing skin off the Bridge of my nose after a long day of shooting. Not any more

I buy this for my Sony EX3

I have glasses and I had a lot of problems getting smears on my glasses from the rubber eye cup of my camera. I use both a Broadcast TV camera and a cinema camera. This is a soft solution to protect your eye and glasses from the smearing of the camera viewfinder.
The company recommended the Ultrasuede version for people that wear glasses. It is working great for me.
It is not easy to get this on the rubber eye piece, but it's not as bad a others have mentioned. The existing rubber eyepiece goes in between the layers of the Bluestar Eyecushion. The first step is to get the larger portion of the rubber eyepiece through the smaller round hole in the back of the Eyecushion. Then feed the rest of the rubber eyepiece into the hole between the back portion and front portion of the Bluestar eyecushion. Just work your way around until all the rubber eyepiece is in. Then adjust it for position and fit. If you bump it or pull on it, it will come off again. It probably takes a minute to re-install.
It has kept my glasses cleaner while working.
The Oval Large was recommended for a full size broadcast camera viewfinder with the oval rubber eyepiece. It may look a little small, but it fits just fine. You want it to fit tight without a lot of play, so it stays on.
I'm glad I purchased it, I have 4 of these now. One for each camera and a couple of extras when they get too dirty. I'm going to try washing it as see if that works.

Very comfortable and appears durable over these early days. Washing carefully seems ok. A snug fit on the Z-Finder. Certainly looks like chamois.

Bluestar makes the best eye cushions. I have a smaller one too and it works well for all different types of viewfinders. I didn't think it would make a difference, but using one really helps increase the comfort level when using the viewfinder on your camera. The price is affordable too.