Make sure you have a reservation before you go. They will turn you away without hesitation.
https://gostateparks.hawaii.gov/diamondhead/about

Here are my reasons for staying at Centric:

To use Cat 4 cert.
Savings over $50 per night vs HR for Globs; if we remove club/breakfast conversation, any saving is a good saving here.
Time spent mostly exploring the island and not Waikiki area. No reason to hurry back, no club here.
View is not important.
Shorter walk to Marugame Udon.
Dont mind the kiddy pool depth pool.
Descent hot tub.
Sun tan and after sun lotion (pre Covid experience) on the pool deck that HR offered in ABC store for sale.
Trying to impress family with my driving skills. If you rented a large SUV or van, might want to double check your insurance deductible and coverage.