A reverse mortgage is available only to homeowners that are at least 62 years old.  An Unlock Agreement has no age requirements.  Depending on your circumstances an Unlock Agreement can yield more or less cash to you up front versus a reverse mortgage.  With a typical reverse mortgage, you are required to pay off your existing mortgage at closing in order to qualify.  With an Unlock Agreement you are not required to pay off your existing mortgage.
In addition, a reverse mortgage is a loan and has an interest rate which increases the balance owed regardless of the home's value.  Over time it is possible for a reverse mortgage to consume all of your home equity.