These classic-style balls can be used as kegel exercisers, worn around to enhance arousal, or kept in during penetration for added sensation.
As a kegel exerciser, they are best suited to an advanced user. They're meant to be inserted, and then squeezed with the vaginal muscles. I for one cannot hold them in for long when standing, so it's something to work up to.
As arousal enhancers, I did have a good experience wearing them for a long car trip. I put them in right before I left, and squeezed them during my drive. When I got out of the car I was very wet, but that just made it easier for them to slip out. I guess they did their job and were ready to take a break!
Lying down, I have no problem with them staying in of course. I can do kegels this way, or keep them in for added sensation during sex or when using a toy for penetration (my silicone vibrator is great with these). My main partner likes me keeping them in, but another one is put off by it since as he says "it feels like I'm playing pinball in there". Next time, I'm just going to play "Pinball Wizard" and see if that gets him in the mood.
The packaging says these are "for vaginal or anal pleasure". NO THEY ARE NOT! Don't listen to the package! Do not put one of these inside your anus! There are plenty of toys for that - they have flared bases or handles so they won't get "lost".

These are made of a nickel-free metal. They are smooth and hard, and if you like temperature play they can be cooled down or warmed up before insertion.
Because they are smaller and heavier than other options, these offer a challenge. I would categorize this as an advanced toy, since anyone newer to kegels and muscle control will do better with something larger.

Even though this is the "classic" style of ben wa balls, I really prefer some of the other options out there. I also have the duotone balls [https://www.edenfantasys.com/sex-toys-for-women/kegel-exercises/duotone-orgasm-balls] and although they're not perfect I prefer them for a couple of reasons I'll go over when I review them.

These balls are 3" around, and although the packaging says they're larger than "regular" balls I still find them to be too small. Here's what they look like compared to a lipstick and a quarter:
[https://cdn2.edenfantasys.com/Images/CustomerImages500x500/634790743908263750.jpg]
And here's what they look like compared to the Duotone balls I mentioned:
[https://cdn2.edenfantasys.com/Images/CustomerImages500x500/634790744395607500.jpg]

The one possible plus is that these may be good for someone who is very small or tight. Users new to inserting anything into the vagina may find these easier to start with.
Users who have really built up their muscle control might appreciate the challenge these offer.

Even though these didn't cut it for me, I don't completely hate them. They are good for wearing when I'm sitting or lying down, and I like the cool feeling I can get by holding them under running cold water before inserting them. I also found out that I like the way they feel when rolled over my clit. The weight is their downfall when I'm trying to walk around with them, but it makes them feel really good if I just roll one around on and around my clit. I have had an orgasm from that, and I'm happy about any kind of orgasm!
One thing I noticed when I do have these in is that they're not as noticeable as some others. Even though they're heavy, they are solid. Balls that have weights loose inside of them do a lot more for me since I can feel more motion when moving around.

Easy to clean, care for and store. The balls can be washed with soap and water or put in the dishwasher (in the cutlery basket).
Metal is safe to use with any lube and can be stored in pretty much anything. I keep mine in a small box but they could be kept in the mesh pouch they came in or loose in a drawer or toy box.

The box these came in is not at all subtle since it says "orgasm balls" right on it along with the usual sexy model picture. It also says they are for vaginal or anal use, which is not correct. They should not be used anally at all. I know they have the standard disclaimer about being "for novelty use only", but I don't consider than an excuse to suggest an unsafe activity right on the box. Eden users have a wealth of information available in the forums, but not everyone has access to such education, or thinks to seek it out. I consider the box copy irresponsible, and yes, I know I'm going on about this a bit but safety is essential to a happy and fun sex life.
Inside the box, these balls are in a lavender mesh pouch. I thought the pouch was kind of cheap and haven't used it for storage, but it could be.