This is a set of nice, decorated nipple clamps that would probably be good for beginners. You can adjust the pressure using the screws, within reason; the clamps can only go so tight, and past a certain range, they won't stay on. The lighter end of the pressure range will vary depending on the size and shape of your nipples.

The packaging suggests using the feather attachments as a teaser before putting the clamps on - sort of like a mini feather teaser. I found that the sensation from the feathers was too light on my breasts for me to feel much, but I usually prefer "deeper" sensations. If very light surface touches work for you, this would be great!

The clamps themselves can be used on the nipples in a couple of ways: flat against the breast, or sticking out, away from the body.
Using them flat is probably a good idea for beginners, or people with very sensitive nipple. That way the pressure is spread out over a greater area and there's less of an "ouch".
If your nipples are less sensitive or you prefer a more intense pressure, attaching the clamps so that they point out from the body will cause more pressure on the nipple, as there's less surface area in contact with them.

If you're looking for a really hardcore clamp, you may want to look elsewhere. These only go so tight. "Comfy" seems like a strange description for a toy that's meant to cause pressure or even pain, but that's the best description I have for these clamps: the feathers are soft and nice to touch, and the rubber sleeves go easy on your nipples.

The clamps are metal, with a rubber sleeve over the pinch-y part (that's the technical term, I swear). The feathers are rooster feathers dyed black.

I didn't care much for the feathers, but it's more of a personal preference - I don't really like the feel of the "stems", but that's not much of an issue for the soft tips that will touch the skin most when worn, and when used as a teaser. I may end up removing the feathers, though it seems like a bit of a shame.

The clamps had a very light plastic odor, mostly from the feathers. This may just have been from the packaging, and it has already faded somewhat within a day.

The most important part, in my mind, is the rubber sleeve on the clamps. It's smooth and firm, but with just enough yield that I didn't get any (bad) pain from the clamps. With the screws adjusted for a light pressure, the clamps were very comfortable to wear, thanks to the rubber sleeves. If you have rubber allergies, they could potentially cause some issues, but I think for most people that won't be a problem.

I found the style and features of these clamps comfortable and easy to use. They're simple to put on - just pinch and apply! Fiddling with the screw to adjust the pressure will only take a moment.
I think these would be pretty obvious if you wore them under clothing. The size and style of the clamps will lie almost flat against the breast, but they still protrude, and the attached feathers will flatten down but there will still be some bulk there, as well.

Both clamps have a screw to adjust the pressure: screwing it in further will force the clamps apart and lessen the pressure, screwing it out will make things more pinchy. I'd say you can get anything between mild and moderate pressure depending on how tight you have adjusted the clamps and how you're wearing them. Your position will make a difference as well: if gravity (or someone else!) is pulling on the clamps you can get more pressure out of them.

Since these are adjustable and have a fairly broad area of contact, I think these would fit most sizes and shapes of nipple. I have fairly small, flat nipples and I had no trouble getting these on or keeping them on no matter how I wore them.

These clamps are small and could easily be stashed somewhere discreet, although you'll need to be gentle with the feathers.

The feathers are a little fragile and could break if you're not gentle with them. I was careful with mine, but I noticed the feathers shed a little bit - just a tiny wisp or two.

The packaging on these clamps was sturdy cardboard, and definitely not discreet - there's a picture of a woman, bound and naked, wearing the clamps. (She looks surprisingly bored, given the circumstances!) The clamps were in a small plastic packet inside the box. There were no instructions included, but the back of the box was sort of a suggestion for use in the form of a short first-person story about using the clamps.