I have done fairly regular linking for individual online purchases for a few years. I have not linked other credit or store loyalty cards. Have made about $500. I just got it by check to me, though, didn't bother with setting up child accounts or waiting for college bills. we have 529 Plans set up through another source, so not worth the trouble to me to set up another 529 account to link for college.
Got the Mastercard (with a sign up bonus), but usually use it only for those Upromise-linked online purchases that earn 5%+extra, and at Sam's Club which, last I checked, only accepts MC.
I haven't had any trouble getting the money (I wait until accumulate 100$ or more before requesting check). They don't send too much junk email.