So if they die fast is because they have not much hp, so wound/zap would be a waste aswell.
But charms are not about level but vocation. You will have them for ever in your char, so you have to be smart and buy them thinking about which ones will be more usefull in the future too.
For example, my first charm was 'poison', I didnt think it twice... and it was pretty useless for me after I leveled up a little more. Lucky me, right now I can use it on a creature I hunt daily.