The benefit of using type #304 verses #430 stainless steel is that the #304 is better suited for the harsh environment that a Type I CKV must withstand. The 304 material will better withstand the harsh degreasers and other chemical that are used during the hood and duct cleaning, the chemicals that make up the kitchen fire suppression as well as the effluents that pass through and/or collect on the CKV hood as a result of cooking and kitchen cleaning applications.
The CKV hood should be designed to hold under regular use for up to 40 years. The increased cost of using type 304 verses 430 is a small price to pay for a lot of adding protection depreciated over a 40 year period.