When comparing Rename-It! vs Flexible Renamer, the Slant community recommends Rename-It! for most people. In the question“What are the best bulk rename tools for Windows?” Rename-It! is ranked 7th while Flexible Renamer is ranked 9th. The most important reason people chose Rename-It! is:
It can rename thousands of files in seconds and does it in a single transaction so that if anything fails it renames nothing at all.
Specs
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Pros
Pro Really fast and safe renaming
It can rename thousands of files in seconds and does it in a single transaction so that if anything fails it renames nothing at all.
Pro Can rename the full path
You can change file's directory or rename the full path to the file.
Pro Open source
Pro Can create numbered series
You can ask it to rename so it's Image001, Image002, etc.
Pro Supports regular expressions
Additional to wildcards, and string replacements, it can use RegExp.
Pro Incorporates in the Explorer context menu
Pro Detects cycles and handles them
If you rename A -> B and B -> A (or any cycle), it'll automatically do A -> T, B -> A, T->A.
Pro Command-line arguments
You can create a script invoking Rename-It! from the CLI with some arguments so it performs the renaming and returns the correct exit code.
Pro Can use audio file ID3 tag info
Pro Powerful but easy to use
It has many options, including renaming using tags (ID3, Exif...), can number files, use wildcards or regular expressions, walk a hierarchy of folders.
And it has presets for common renaming tasks, like removing parentheses, "Copy (n)" or "Shortcut of", and so on. Its preview feature avoids errors, and warns (a bit late though) of naming conflicts.
Pro Free
Freeware and lightweight (archive is less than 2 MB).
No install, but might need removing options of Explorer integration / scripting if removing.
Pro Context menu in Explorer
Can add a context menu to Windows Explorer to rename files in a chosen folder.
Pro Tag management
Can rename using ID3 (music), Exif (photo), IPTC (images), DOC or HTML tags.
Pro Has many translations
Available in English, Japanese, French, Spanish and German.
Pro Scriptable
You can write scripts in VBScript or in JScript (native Windows scripting languages) for complex renaming operations.
Cons
Con Dated
Quite dated - last release or code update at least two years old.
Con Seems to be no longer maintained
Last updated in 2011 (v. 8.4). Yet it works fine in Windows 10 and still does a tremendous job.