I'm still setting this up so don't yet have field data on performance, but 4G LTE ping times are about double the latency of home broadband, http://blog.catchpoint.com/2014/01/15/theres-no-avoiding-net....
For me the primary concern is privacy and security and using the always on VPN is the best way I've found to protect what I value.
Nothing gets out without my expressed consent, just the way I like it.
The VPN can drop out when I change networks, but it reconnects in less than a single second under good conditions, and that's not an exaggeration. I use a plain ipsec xauth VPN.
Having tried both ipsec with l2tp and openvpn SSL VPN, ipsec is the only one I can get to reconnect in under a second. All the others take at least 5 seconds to complete a handshake.