Installing an App that is not in the App store is normal.
You buy a car, say a Ford Mustang. You didn't buy it from a Ford dealer, you bought it from some guy selling it on Craigslist. You need an oil change for it. Do you go to the Ford dealer, or just your local mechanic? You do a lot of things in this world without worrying about risk out of proportion to benefit.
Same thing with Apps. App store is source of some Apps, but not all. In a lot of cases you need custom API work that will never be found in an App store App. So you have an App built that does what you want, how you want, when you want, at a cost you like.
