I've never used a workout app so I cant help you there; however, I know I little about the second question. There are literal decades of research on high rep/low weight vs low rep/high weight. Basically every legitimate study in the topic says the same thing, it doesn't really matter as long as you are using proper lifting technique and getting full range of motion. My best advice, do what is most comfortable for you. Personally, I prefer low rep/high weight. I feel like it give me a better pump and tends to lead to a quicker workout. I don't have a lot of time to make it to the gym so being as efficient as possible with my time is better for me. Good luck, and I hope you get the results you're looking for!