With version 2 of the app there has been some complaints that the "Chars from custom string", i.e. the ability of generating random words from a custom set of letters, was disappeared. Furthermore, some also confused this feature with the "Custom string" one, that simply plays the string as is, which in V2 is identical to the one in V1.
Actually, this feature is still available. The previous "Chars from custom string" feature is now "Koch (custom string)" and it is more powerful than before.
Now, you can use the custom string to define a Koch sequence, for example "ABCD". Then, using the Koch letter selector (the [A] icon on the main screen), you can have random words generated using letters "A","B", or "A","B","C" or "A","B","C","D". Obviously, if you select the highest level (all letters) it behaves exactly as the old "Chars from custom string".
The video below shows how it works and how to set it: