My problems started when I used it as a master node in a cluster with 3 more Pi2B as slaves. Nfs4 did not run because of the portmap issue and then I could not install openjdk7 because of the packages missing in the mirror of Raspbian.
It should be okay to install Jessie on the Pi 1. It's compatible now.
Besides, you won't break the Pi if you installed something incompatible. So relax and flash away.
I haven't had any issues still running a full blown Java web application. Been two weeks today.
I can confirm it works on a Raspberry Pi Model B Rev. 2, as well as the Raspberry Pi Zero. I have both of these Pis, and have installed and successfully run Jessie Lite. It works very well, in my experience.