Pros: - Truly the best tinkering toy I have ever played with. The first night I got them I probably logged two hours of time with just 80 of them.

Cons: - The metal coating begins to wear off after hours of use. This is catalyzed by squishing them in the hand, which I've only done a bit of. The coating only wears off on the two ends of the magnets, and these ends only show up when you make a stacked 3D object such as a cube. However, when these ends do show up, they mark up your hands just a bit. The makers of the Neocube, another Neodymium magnet product, warn about possible health concerns if the coating wears off, even though nothing has been proven. I think it's fine, but, it's just something to be aware of.
- I ordered four sets of these in late December and they all fit together perfectly. I ordered another set in mid January when they were back ordered, but they still arrived early than expected. Unfortunately, these new 6mm magnets are slightly larger than the old ones! I don't have a precise measuring device, but it's probably close to 6.3mm or so. While this may sound like a small difference, it's just enough to throw off your entire set's overall shape. I spent a good 20 minutes sorting through old and new magnets (separable from the worn out ends) and now keep them apart. This means I've got a set of 80, which can make a fair amount of small shapes, and a set of 40, which can't do too much. If I want to grow my collection, I'd have to buy at least 60 more.
- The price should be lower than it is.

Bottomline: Although the cons list is significantly more detailed than the pros, the pros here far outweigh the cons, especially if you're a first time buyer. These things are a bliss to play with, and will always keep you entertained.

Pros: Very fun to kill time with.
You can make nice shapes.
People are interested and all want to borrow them from you.
Get more than the 20-pack, you can't make that many shapes out of 20.
Very strong magnets for its size, hard to lose (unless you lose the whole pack together).

Cons: None at all.

Bottomline: I have been playing with them in class for days.
You can even "clip" them on your collar or clothes. Although it gets easy to lose them if you lean on lockers or something you should be able to hear it stick to whatever metal component you were close to since it is pretty noisy.

Pros: - great if you're the type of person who needs something to play with while studying, reading etc.
- really fun to make shapes
- fun to play with in class when you're really bored

Cons: - the packaging with the bubble wrap was a bit hard because it was all taped together
- not a lot so you should buy a couple more of these

Other Thoughts: - you should buy way more because 20 isn't enough if you're planning on actually making something big
- came in red bubble wrap

Bottomline: - extremely fun to play with if you're bored
- buy it (or 5)

Pros: - Fun
- You can make nice shapes
- Not much people have it
- Excellent if you can't sit still when you're studying
- It isn't very usefull but just fun

Cons: - Could be cheaper on other sites the price isn't much more.
- Watch out for little kids, they can easily swallow them.

Other Thoughts: It's just fun to play with.
You can make nice shapes
I recommend buying more of them at the same time because 20 of them is really not enough!
I bought 6 packages of them and i Find that not enough.

Bottomline: If you wan't to make cool stuff buy more then 1 pack!
For the rest it's fun to play with