Yep they come in a handful of sizes. The more common size for these protests seem to be around 2 inches in diameter.
To put that in perspective, try to make the largest circle you can make with your index and thumb (think OK symbol shape). That's more or less the shape of these things and they are effectively a thin layer of rubber with a solid steel core. The inside of your finger circle is the steel and the thickness of your fingers is the rubber.
It does help, thanks, and it's also terrible, because it sounds like the police would think "oh it's fine, these things aren't lethal" and then shoot people willy-nilly with what are basically big steel cylinders.
Some are, usually they’re packed into 12ga shot shells, but those are limited in their velocity due to their tendency to penetrate rather than bounce off the victims. The bigger ones are able to strike further and harder with a reduced risk of penetration.
At the paintball size it’s now more common to see CS filled paintballs. Those don’t require a huge amount of kinetic energy to work, although exposure to CS gas has its own long term side effects.
Those paintballs are filled with oleoresin capsicum (OC) which is a far more persistent and "persuasive" substance. Getting hit with a CS paintball would be ineffectual due to the small amount and the fact that it wears off quickly.
What "long term side effects" does CS have? The US Army (at least) routinely puts all soldiers through a CS filled gas chamber as part of chemical warfare training and has done so for decades.
There are no longitudinal studies, because it is very difficult to find a sample of repeatedly tear-gassed subjects over relatively long timeframes. Hong Kong is a good example though, where estimates are that ~90% of the population have been exposed. In Hong Kong, long-term exposure has been connected with rashes, respiratory problems and chloracne.
I see from another reply from him that herewulf that you reply to has been repeatedly exposed to concentrates cs over multiple years.
eitland has been exposed to concentrated cs at least once, Anigbrowl multiple times including more than just once just this last week and it seems to be common in military training from what I read so I guess it is in fact well studied and reasonably harmless compared to many alternatives.
That said I agree with a number of people here that in most cases the best alternative might be to talk to people instead, and to not kill suspects in custody, obviously, and also to not handcuff and throw people on the ground when all that should be necessary was to ask simple questions.
It’s only the less effective shot shells that are more likely to bounce around and be hard to track.