Snails are great pets to keep and once you start getting into them, they can be quite addictive! They do not take up much space, they make virtually no noise and there is no pet hair to hoover up which makes them perfect for someone with allergies.
There are so many different species, all over the world, each with their individual likes & dislikes... Some eat only plants, some are carnivorous. Some are only 2mm in shell length, others can get to over 12 inches. Some have amazing shell patterns & colours, others have a plain coloured shell but beautiful body colours / markings.
Most Snail species are fairly active & fascinating to keep providing that they are all kept in their own tanks & tubs in a habitat suitable for that particular species. (Some species are more challenging than others & will require extra time & care)
For anyone with a pet hair allergy they are ideal, however if you are thinking of snails for a child's pet you need to be aware that children get bored easily. Please remember that it is perfectly natural & not to criticise them for it. I would first suggest getting one from the garden for a while & helping the child find out how to care for it properly, to see just how long the attraction lasts, as it can then be set free if the child gets fed up with it. You can always progress to a non-native species if the interest is long term.
I can certainly recommend keeping snails as a hobby & they really do make great pets as long as they are kept properly and bred responsibly, with any unwanted eggs being frozen.