Unlock River and unlocking a GSM Samsung S4 - is a fee service worth the cost?

Factual Questions
1

I need to unlock a Samsung S4 and have little specific experience at this. Unlock River will generate an unlock code for $40. Is it worth it? Is it a rip off? Does the phone need to be altered first (or rooted)?

I am willing to pay the $40 if it works and is reasonable.

Thanks.

2

I used Cellunlocker.net to unlock a LG on the AT&T network. Fast service and cheaper than Unlock River. $25 for the unlock code.

But first, read their advice and instructions to make sure you can do it. Cellunlocker Samsung instructions.