I use Ralgro. One thing you want to make sure, if you keep back heffers as breeding stock, don't implant them. It says so on the box. There is a type of implant you can use on them, but I just don't implant replacement heffers at all.
I had my vet explain it this way. If you implant them with ralgro once in a heffer, you will delay puberty on them, they may become breeding stock eventually, but it really messes with their bilogical clock. If you implant them twice, you will delay puberty on them permanently.
I don't know how effective it is, but it's not terribly expensive. I do it because my dad always did. I have a neighbor who feeds out yearlings, and he implants them as often as he can according to the label.