As I understand it, there are a couple of differences between the friends & family program
and the guest shopping link.
When someone accepts your friends & family invitation, they do have to sign-up for their own accounts (if they don't already have one) and add you to their beneficiary list in order for you to receive contributions from them. The advantages to this program are that your invitees can accrue savings from all of the Upromise programs and, once the contributions are funded, your allotment from their savings automatically transfers to your account every month.
The guest shopping link, however, is limited to the online shopping program. In this case, the eligible contributions from anyone's purchases using your guest link should post directly into your account. The advantage to this program is that you can post your link on any social networking sites you belong to so that anyone can use it whether or not you know them personally. It's also a nice option for anyone who wants to help you save, but doesn't really want to open a Upromise account of their own.
There's no reason why you have to choose one option over the other. You can actually take advantage of both programs to maximize your savings.
I hope you find this helpful. 
