I just looked at TETHR for the 1st time, didn't dig too deep yet, but i'll look into it.
I didn't see what you actually get from them, it says "app screens for demo" so do you actually get the source code? Are these templates for some other product?
If you don't get the source code, I'd pass on it.
There's other sites that offer complete code or what I consider best, is a tutorial that teaches you how to program it from scratch or using a 3rd party tool.
I see you're new to app dev. Apps can be programed a number of ways. You can download xcode and write programs in ObjC/Swift and you can add on 3rd party tools to do things or just use it out of the box.
You can also use engines that do things like game engines (Unity and others). These can work inside of xcode/objC/Swift or they might be stand alone tools like Unity.
TETHR looks like it has ready made projects that you can modify to fit your needs. These might be in the form of templates and could be well done, save a ton of time and can be a great learning tool.
I use a number of 3rd party tools for RSS feeds, slide out menus, database, etc...
One downside is that they might not have good support, they might not be updated to the latest versions of whatever Apple puts out and tutorials might be hard to find.
Unity has books and tons of tutorials because it's popular. The slide out menu I use didn't have but a few tutorials.
GitHub has a whole bunch of these add on and there's sites that list off a bunch with an overview of what they offer.
Before you get too deep into any one thing, I'd search for tutorials and look for what kind of support it has.
You should evaluate your goals, are you looking for a job or an app or just a hobby?
Does the add on product give you the source code? If so, it can be a great learning tool.
I, personally like the Ray's site for tutorials
https://www.raywenderlich.com/category/swift
[doublepost=1475045731][/doublepost]I can't find anything on TETHR about getting the source code or even any other sites that have it.
I also noticed that they have a "sell your product" on the menu. So it looks like a place to buy other people's work. That's not bad, but what do you actually get?
I'd want to see the actual source code.
If you don't get Swift or ObjC source code, I'd look at buying the source code from someone else's app or do some tutorials.