[eluser]WanWizard[/eluser]
You should avoid storing any user data client side. It's not secure, and the storage is very limited.
I never had issues with database sessions, even on high traffic sites. It's one read, and one write (you need to extend CI to get that, by default every session update is a write), on the total query time of a page request it's not much.
If you don't feel like it, you could switch to native sessions, which uses file storage. You can combine that with a caching mechanisms to speed it up even further.
