This plugin allows you to put in a full path URL to redirect mobile traffic to.
First, check if this is happening on another computer. If not, the redirect is simply cached on your machine. Clear the cache and you should be fine.
If the redirect remains everywhere, check if there are other redirect scripts running.
(v1.1) Yes, but mobile users will be stuck only viewing that page as the plugin will redirect them back there if they navigate away.
You will still need to use a full path as well, and make sure the URL is exactly as what will be redirected including / at the end if necessary. As of v1.2, you can use the Redirect Once option to redirect users to an internal page on their first visit, afterward they'll be able to browse the site normally.
Yes, there is an option to redirect all tablet traffic.