I've had this battery for months now, everything is fine, very easy to replace, but if you are insecure check youtube tutorials first so you have an idea of how you should do it, then check again the tutorial when you replace it.
The time it lasts depends on how you use your iphone. But I'd say it lasts about the same as an original battery would. I spend a lot time playing Fifa 14 online on it, something that make the battery go from 100% to 0 very quickly (about 4 hours), played it many tomes but when I don't the battery still lasts for a good time (a day), so its not addicted I'd say. The price is excellent, so I'd buy this again in case my battery gets addicted in the future, I know it would be my fault because of the way I use it and my habitats of unplugging it while charging, not letting it charging 100%..... But so far, 2 months, its still working fine, which is excellent