From what i know, Diamond current advertising on the natural media used in their filtration system. FYI popular filtration system like 3M, Amway and Aquaphor uses Carbon Block system which is made of coconut shell = natural media also.

Why Diamond require many cartridges because they are giving granular carbon block while better filter will give carbon block (compressed carbon). 1 cartridge of carbon block is better than 5 cartridge of granular carbon.

depending how good the quality you wanna get. For me, quality wise i will get either one of these

1) Aquaphor crystal eco (RM 1500)
2) 3M DWS 2500 (RM 2900)
3) AMWAY Espring (Estimated RM 3,800 need to ask amway seller for latest price)

Maintenance cost per year
1) RM 450
2) RM 900
3) RM 500 (also need to check with amway seller)

I am only selling 3M and Aquaphor, between these two if u ask me i will say get Aquaphor Crystal Eco