you should add the use statement

I think we can rephrase this a bit (and also link to thechoice_list option):

..tip::    When the values to choose from are not integers or strings (but e.g. floats    or booleans), you should use the `choice_list`_ option instead. With this    option you are able to keep the original data format which is important    to ensure that the user input is validated properly.

I'm not sure if the part about database updates is that important. What do you think about this?

I don't think the doctrine update should be mentionned. It is not even the main issue. There is worse than the noop update: in case of edition, the wrong value will be initially selected when using the wrong type, because Symfony uses strict comparison to choose the value

Well I am unsure about this. However as a side effect you have those updates which might cause updated timestamps, called listeners just based on an altered value. I have added it again to raise awareness, however I am fine with removing it. You guys can decide.