Never used the newer ones that are sold, but we always injected things into our roasts and chickens, etc. when I was younger. My grandfather used to make a marinade and inject it in, and boy, was it ever good!

I did see Julia Child do a turkey (and then MS did one)by putting her hands under the skin and loosening it from the meat when the bird was raw, and then pushing flavored butter in and massaging it all over the meat under the skin. Looked interesting enough to try, anyway!!