Should I Use Localstorage?

Local storage provides at least 5MB of data storage across all major web browsers, which is a heck of a lot more than the 4KB (maximum size) that you can store in a cookie. This makes local storage particularly useful if you want to cache some application data in the browser for later usage.

Is it bad to use localStorage?

Local storage is inherently no more secure than using cookies. When that's understood, the object can be used to store data that's insignificant from a security standpoint.

Is it good practice to use localStorage?

Now about the main question, it's not terrible practice, but it's not exactly good practice either. localStorage, just like cookies, shouldn't be used to store private information. Storing an email address is not as bad as storing a password or a credit card number, but it's still private information.