InstaSize seems to only be capitalizing on the success of Instagram without bringing anything to the table. It's a photo editor in name, but it doesn't really do anything.
The goal of InstaSize is to find the "perfect" size for your photos. In reality, it just shrinks them a few pixels without even caring about the content of the picture. When you tap the button to "resize" your photos, you're hit by an ad before the app gives you results. Ads actually tend to litter the app and take up plenty of screen real estate. When you go to the app's settings menu, all you get is a request to rate the app instead of seeing any advanced settings. You can purchase an ad-free version of the app that claims to be faster. Considering how the free version of this app performs, we wouldn't expect much, though.
InstaSize doesn't really do much, and fails at the one thing it actually does try to do. Skip this app and download one that will actually edit your photos instead of just slamming you with ads.