twiml_template version 2 allows you to use twilio-ruby version 5.28.0 and up.
Under the hood, Twilio::TwiML changed from being based on builder to its own class with distinct Twilio::TwiML::VoiceResponse and Twilio::TwiML::MessagingResponseclasses.twiml_template` version 2 gives you all the templating and flexibility of version 1 by unifying the two classes under the template and allowing you to write your TwiML voice or messaging templates in the same way.
Upgrading should be painless, aside from any changes that happened in the underlying twilio-ruby TwiML generation. Look out for
twiml.say message: 'This will be said'replacing the old
twiml.say 'This will be said'