input on invisible fence?

Welp, I have some neighbors who've tried it and said it was a great thing. Others said they didn't want to "shock" their dogs. Still others said the dogs don't get shocked but rather hear a high-pitched warning sound as the get closer to the wire.

Figgered I'd check into it in an effort to be able to still let our dogs run as much as possible but w/out the worry of them ending up on the Interstate.

Anyone have any input on this? Good results? Bad results? If good, have a good inexpensive source? How much range do these things offer, etc?

Thanks.