Before you choose to sign up for Twitter blue I think it’s important to cover some information in order for you to make an informed decision on whether you think it is worth signing up with Twitter blue or just using Twitter.
Twitter is NOT changing to an all paid subscription model, you will be able to continue to use Twitter for free as you have done before however Twitter blue just gives you an additional features that is not available when you’re using Twitter for free.
The only official way that you will be able to sign up for Twitter blue is by using an iOS Device i.e. iPad, iPhone and installing a Twitter app from the App Store, be logged into Twitter and being in one of the following countries: United States of America, Canada Australia and New Zealand at this time. (Source: https://help.twitter.com/en/using-twitter/twitter-blue
Twitter Blue is a reoccurring monthly subscription in order to use Twitter.