What's the difference between the iphone 5 and its clone called the MTK6515 i5?

- are there any big differences on the clone model

- can you still go on the app store on the clone model

There's no such thing as an iPhone clone.

There are genuine originals and there are cosmetically similar replicas which usually run an old version of Android, if they run at all. They are designed and made solely to look and function similarly enough at a casual inspection to get fools to part with their money.

If you want an iPhone, buy a genuine iPhone: used examples are a bit cheaper and if you can't afford one there are plenty of excellent alternatives running modern versions of Android or Windows Phone 8, and BlackBerries also offer worthy alternatives. All four operating systems have their relative strengths and weaknesses, and the main weakness of iPhones is that their OS is now looking and feeling extremely dated, even with the latest skin-deep revamp.