If you plan on playing around with it, do it over carpet. Spent like 30 min looking for like 4 balls after my magnet chain weakened enough and they all dropped and scattered everywhere. It's pretty cool, comes with a little case.

would you rate it 5 stars?

4 stars.
It's kind of hard to get the magnets between the ball bearings and the individual cylinders to behave how you want.. but hey, that's magnets. I also expected something better to hold the ink cartridge part of the pen while you are playing with the magnets and the ball bearings, but it's just a little piece of thin plastic.. like what holds a toy on display around the cardboard.
The container itself is cool though, it's all black and is also magnetized.. so if you drop it, it should splatter everything in multiple directions and start a scavenger hunt.
The ink cartidge it comes with is wide, about .75 cm, so if you lose that or need a different color, you can just jack another one from pretty much any clickie-pen around and use that. You'll have to adjust the length with your number of magnets since another piece for the back end that keeps pressure on the point of the pen while you write, but it comes with like 3 other doohikies that help you adjust, and even the clip is

removable, so if you need an extra 10 mm you can adjust it with that. That trick took me a few min... the pen was just off and the last magnetic part would go... diagonal lol.
It also comes with a little pen cap, but that thing is so small I'm surprised I didn't lose it in the first 2 minutes.
Downsides: + and - being labelled would help immensely. You try and build something and if you don't test it with.. like a key piece that has one of the doohickeies to adjust to ink cartridges to test it on, you run the risk of trying to add a magnet and utterly fucking up what you already have because that repelling end is going to send the rest of your build in unpredictable directions.
The ball bearings don't stick after 5ish in a row, and they are different sizes. I haven't tested if you can push it out further by going big/small or small/big because they keep wanting to form triangles, but it's really hard to build a chain out of them.... I was going to build a dude with like a

ball-chain whip. Didn't work.

So... 4/5. A cool toy where if you had an office job I can see immense pleasure derived... but for now it's just a cool little gizmo I've collected and might bust out for lame magic tricks.

About the case... it's a black rectangle, but the plastic thing I was talking about fits inside. I wanted felt or something.

maybe not felt.. idk what that would do to the magnets... but.. just not literally the cheapest plastic possible. I just threw the plastic away and put everything in the rectangle box to do it's thing.