Just a heads up that services like these won't work behind security-aware DNS recursive resolvers (like OpenDNS) or routers (like Google Wifi) that block DNS rebinding attacks.
EDIT: I experimentally confirmed that opendns and google dns, which claim to block dns rebinding attacks, do not block xip.io or subdomains thereof
I have just checked, and my pfSense firewall (which claims to block DNS rebinding) blocks local addresses from resolving through xip.io (tested with loopback and several RFC1918. All blocked, regardless of whether they match the subnet in use). External addresses (e.g. 1.1.1.1.xip.io) resolve fine.