This plugin is very powerful and the repeatable field groups are an amazing feature. The functions offer lots of flexibility for extracting information.
I did run into some snags extracting file info, especially for repeating file field types. The arrays did not return some basic file info such as file name. I had to use some of the WordPress built-in functions like
basename(get_attached_file(754)) to look up an attribute by post id. I also ran into some difficulty creating extended_return_values arrays for repeating file field types.
I also ran into an issue where null values were returned in key-value pairs called by the plugin's built-in functions. This seemed to occur whenever a field or a field's value were deleted. I had to create a custom script to handle these.
On a positive note, this plugin is a simpler and more affordable alternative to the
Advanced Custom Fields plugin, which charges for some of the advanced features that
Simple Fields offers for free (like repeatable field groups).