I used it a bit when I lived on the island. Not often because it was on the wrong side of the island and there was a bus service on our side of the island. Nowadays there is no train and no bus on what was our side of the island.
Recommend walking or cycling the Hayling Billy Trail from Havant station, couple of good pubs by the waters edge at Langstone. Walk from the old Hayling station (goods shed now a theatre) to the ferry for Portsmouth. Then catch the No 25 bus to Portsmouth Harbour station. You can also do a circular walk/cycle of Langstone Harbour
https://www.haylingferry.net/cycling, about 14.5 miles