TinyUmbrella 4.21.12 is out with beta support of the nasty 4.2.1 recovery loop fix. I've finished the OSX version and am currently working on the windows version. As soon as the windows version is fixed, I'll update the links.
In order for the 'Fix Recovery' button to be enabled you must put your device in DFU. Once the 'Fix Recovery' button is enabled, click the button then click 'Yes' on the confirmation and wait. Your device should reboot out of the recovery loop!