When comparing Tk vs Flutter, the Slant community recommends Flutter for most people. In the question“What are the best cross-platform GUI toolkits?” Flutter is ranked 11th while Tk is ranked 12th.
Ranked in these QuestionsQuestion Ranking
Pro Bindings for several languages
Bindings for Python, C, C++, Ruby, Perl, Go, Java, Haskell and more, see Languages with a Tk binding.
Pro Easy Styling
Once you understand how to style, the styling can look great
Pro Great for beginners
Easy to pick up and run with it.
Pro Open source
Pro Great developer tools debug/hotreload/analyser
Pro Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers.
Pro A single codebase for iOS AND Android
The developer's goal is to allow people to make apps running at 120 FPS.
Con Base looks are garbage without a good amount of styling
Going with the base look for your app is a bad idea because it looks like garbage with the defaults
Con C# support lacking
Although the Eagle Project exists, which offers Mono and .NET Core support, C# support is not standard.
Con Still in development
According to the website, Flutter is still in its early stages of development.
Con Based on Dart language
Dart is a Java like language, easy to learn and startup fast for millions of Java developers. BUT if you have to learn it ... it's a con.
Con Dart is unpopular and never gained serious community traction like Kotlin or Java
Con Does not support 32-bit iOS devices
If you plan on targeting iPhone 5, 5C or earlier, you can forget about Flutter.