Switching to another user does not work at all. To bad cause it's in some cases important to switch users when still logged in as an administrator.
This plugin is great if you want a option to go to the login page on your website, so you can log in as another user with the username and password.
With the other one, one had to log on with the username of the target user, using the admin password. Logging on as many users became a big thing.
This plugin, however, does not require any password to be entered. Once logged into the backend, you just click the target user, click the button to log on as that user, and bang, you're in as that user. Excellent!
If you're more into typing than clicking, you might prefer one of the other extensions, though.