Instaling app without AppStore, Jailbreak or any warranty void itp.? I have a question. I'm developing an app for iOS. I don't have a subscription of Apple Developer Account(I'm thinking about buying that but I'm hesitating because I don't know whether my app will work or/and be published). 

Are there any reliable and legal ways for my friend to install it on his iPhone without jailbreak, AppStore or any warranty void itp.? Is Cydia Impactor safe under above conditions? Is Apple going to make trouble when they detect that an app was installed with this tool?
A person can deploy apps to their own iOS devices using Xcode without a developer account, and without breaking/modifying the OS.  All one needs is an Apple ID, and a Mac running a recent version of Xcode (7.3.1 or later).  This is an Apple approved method of installing apps (designed for educational purposes).  Xcode will generate the needed personal provisioning profiles automatically.  

You can search for instructions online (here are a few examples: Xcode 7 develop for iOS without developer account and http://blog.ionicframework.com/deploying-to-a-device-without-an-apple-developer-account/ )

Apps installed using personal provisioning will be time limited (expire in somewhere around one week to one month).