What is IKEv2?
IKEv2 stands for Internet Key Exchange Version 2. While IKEv2 is technically not the name of the VPN protocol, you will find it as a separate option in the ExpressVPN apps. In these cases, IKEv2 refers to a L2TP/IPsec implementation that uses this newer, more secure key exchange protocol instead of the older IKE.
ExpressVPN recommends you to use the OpenVPN and IKEv2 protocols. While L2TP/IPsec still offers encryption, there may be ways for an attacker to decrypt the VPN session.