Is it safe to install Android L on my Nexus 4 (January 2015)
Wait.

I've had positive and reliable experiences running Android 5.0.1 on Nexus 10, Nexus 7, and Nexus 5.

However, my Nexus 4 experiences reboots with Android L and a friend's Nexus 4 outright powers down regularly.

That said, a bugfix Android 5.0.2 is rolling out to Nexus devices right now.  So wait.