Secure delete device for resale.

I am done with Apple mobile products, and have upgraded to new Android devices. As such, I would like to sell my iPad 1 and iPod Touch 4th gen devices to someone who actually wants them. As part of that though, I obviously need to delete all of my files off the iOS devices, which is where my questions are. Number one, is that if I click erase all settings and files in the settings application, will zeros be written over all of my data, or does iOS simply unsecurely "trash" everything, leaving the next owner the ability to easy see all of my data? Some people are saying only older devices are secure deleting files, while other users are saying no iOS device does that. Number two, is does the older iMessage bug that sent iMessages to deactivated devices still happening? It seems like the bug was related to iPhone's though SIM cards, but I would like to make sure.
Thanks!