What are some alternatives?
When comparing DownloadIG.com and PostDownloader.com, you can also consider the following products
GramPhotos.com - View Instagram Full Size Profile Pictures
GramDL.com - Instagram Photo & Video Downloader
GramDownloadz.com - Instagram Post Downloader
4K Stogram - Free Instagram Downloader for macOS, PC and Linux. Search, download or backup Instagram photos shared by any user. Follow your favorite photographers and stay tuned!
GramSaving.com - Download & Save Instagram Posts
JustForLink - Simple way to download photos from Instagram to your Mac, PC, tablet or phone from any browsers.