I think you should extend it to Kwun Tong Town Centre because in Hang Hau the only bus to Kwun Tong is 98A, which has to go via Po Lam Road. Also, no buses from Hang Hau uses Tseung Kwan O Tunnel.
98E can provide a faster and more efficient route for Hang Hau residents by using the Tseung Kwan O Tunnel. Also, they can take this route to Tseung Kwan O Interchange Station to change to other routes. Therefore, you can kill two birds with one stone.