One nit: the all-in-one toolkit I used fails to re-root the phone once it's running Jelly Bean. Other more detailed recipes also failed.

Then I found this excellent tutorial for rooting Jelly-Bean from somebody with similar problems.

Why root? Well, I needed it here so I could run AdFree to kill off the in-app advertising from certain other useful apps. This program updates /etc/hosts, which requires root access to do.

And finally I discovered that "adb" (or adb-linux) is the way to really get into the handset. Useful, that.

Cheers