Hi Donna,
Just because an addon is listed as supporting Moodle 2.7, it does not necessarily mean that it will not also work with Moodle 2.8+. Many people run at least two copies of Moodle. One for their production site and one for testing things such as trying addons. It would help to know which addon you are interested in as possibly someone has already tried it on M2.8 and could answer you question for you.
HTH,
AL