I've been using it since my Palm Treo days, long before the iPhone even existed.
I like it because it allows me to use it on multiple IOS devices and allows me to sync and backup with its desktop application. Now they have the option to sync via cloud (costs extra subscription fee), but the basic version is good enough for me.
I've used 1Password since I got it for my iMac in 2008 with one of those Mac Bundles. I have no reason to switch to something else--works just the way I want it on my iMac, rMBP and iPhone. Great program.