You should only let another person generate a vanity address for you if it is one that involves more than 1 private key (generally referred to as M of N signature addresses which start with a 3 rather than a 1).

Unless the prefix you are wanting is longer than say 5 characters you would be better to generate such an address yourself.

If you are worried about using "vanitygen" then I would advise generating your vanity address on an "offline" computer (and building the executable yourself from the repo source).

Also note that although I do use a vanity address myself it is never a great idea to re-use Bitcoin addresses.