I'm about to change out the chassis batteries in our Allegro. It has Interstate 31-MHD batteries now. They are original to our 2012 model so I'm thinking they were installed in 2011 making them 5 year...
They are more likely just Sealed Valve Regulated, not AGM, Just maintenance free. however you said you are getting ready to replace at 5 years. That argues for AGM (My Maintenance free nearly lasted twice as long, 9 years)
That said however nothing wrong with AGM's. They are decent starting batteries (Save for Optima, and in some cases Optima are best, otherwise they are just expensive).
the major disadvantage in this use is cost. .They cost more, and no benefits.