There are many differences between the two models. Attatched are links with all the info on each model.
The 396 is a handheld that was discontinued maybe 2009/2010. It won't decode DMR NXDN or P25 Phase 2. It came in an Australian model also which was UBCD396T
wiki.radioreference.com
The 536 is not a preferred choice on simulcast but many users have had no issues. Its a base/mobile. It will do DMR, NXDN and Provoice with paid upgrades. It will do P25 phase 2. The AU version is UBCD536PT
wiki.radioreference.com