The TPD also requires stuff like leak resistance and glass protection, which is why a bunch of those tanks are coming out with external metal sleeves. There will probably be more top air tanks coming out as it's a lot easier to present those as "leak resistant". I believe the same "save the children" standard came up with a 2 ml tank/10 ml bottle restriction along with the 20 mg max concentration to try and assure should any actually be ingested, it would be below the severe poisoning risk if a 3 year old chugged it.