The update should be to 3.12.1. It has worked problem free on my Glo, Touch and Aura H2O. The
changes in 3.11.0 are significant and worthwhile.
3.12.0 has a couple of good changes and
3.12.1 just two fixes. Each of those threads have discussion on problems and some other changes people have found.
I say go ahead. If you are buying books from Kobo, then you need to do the update sooner or later. If you want to delay the update, you can connect to a PC and delete the update files before they are applied. But, the next time you do a sync, the update will be downloaded again. Or you have to patch the firmware to prevent it.