For basic data input, I find the app easier overall. It took me a bit to get used to toggling between app and laptop or desktop though because things don't perfectly sync in real time like they do with ht iSS platform or MF.
If you started in one format and switch to the other, you may see the dialog box asking you to choose which version you want. Don't think about WHAT you just did or WHERE. Always choose the newer version as you go back into it. But then ideally, you won't work with many interruptions and have things incomplete to get that prompt.
I also tend to do what I can in-app, especially if any reporting is a basic pick box, minimal or optional comments. I like the red alerts that cue you visually for what is missing at the left margin. When you do it all in the desktop, you do the check and you get the prompt that something is missing, then it can be like searching for the proverbial needle because you don't get the red flags there like a Sassie.
It is through apps that I began to get into mystery shopping more. My first smartphone was a Windows phone, an HTC which I loved. The software did not fight my natural abbreviations and give me goofy autocompletes like Android does in my texts.
When I went Android, I had an HTC first and now have LGs--two of them--which I love.
I still use apps a lot with those little gigs because they add up at the end of each month and can be a no-brainer way to round out a route if you are there already or just pick up some odd cash while out doing your normal errands or shopping.