My preliminary analysis for the iPhone and iPad operating systems is that users should not update to the iPadOS 13.4 or iOS 13.4. Issues encountered by writers for Tom's Guide and Forbes include Bluetooth connectivity issues, a VPN security flaw, cellular connectivity issues, opening and updating apps, and problems with the Control Center. Now, I myself have not had any firsthand experience with these problems (I'm still running iOS 12.4.5 on an iPhone 6), but I cannot recommend to any users of the iPhone or iPad to upgrade until further reports show that these issues are fixed.
See the below resources for more information:
Tom's Guide Report