What are some alternatives?
When comparing Mass Image Compressor and FastStone Photo Resizer, you can also consider the following products
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
XnConvert - XnConvert is an easy image converter for graphic files, photos and images available on Windows...
ImageOptim - Faster web pages and apps.
Squoosh - Compress and compare images with different codecs, right in your browser
FileOptimizer - FileOptimizer is a lossless file size optimizer supporting AIR, APK, APNG APPX, BMP, CBZ, DOCX...
Phatch - Phatch = Photo & Batch!