I have used both, got farther with Chinese Skill (got it first).
That depends on how much time you spend using them and how deep you go. Will those apps alone make you fluent in Mandarin? No. But can they teach you quite a bit? Yes.
I had heard the phrase 谢谢 (Xièxiè) long before I started learning Chinese. Could I be understood at that point if I said it? Yes. However, my pronunciation really wasn’t very good. I spent quite a while practicing it with feedback from a Chinese person and learned to keep my teeth closed and have my tongue positioned in a certain way and it got better.
Likewise, you can probably learn many of the phrases from the apps to a certain level. How high that level is depends on how deliberate and intent you are with your practice. In the end though, for your pronunciation, you are relying on your own ears when using the apps.
Even if you know what you are trying to say, the other person may not.
It can help a lot more with pronunciation to get feedback from a native speaker.
So you can listen quite a bit and learn some written language with the apps and even develop your speaking by copying what you hear.
You probably want to think about the apps as one of the tools you use when learning the language.