untethered jb on 4.3.1 is working fine, if it's your first time jump right in and take a look, 4.3.1 has some programs that just don't work tho
if your ipad is on 4.2.1 and it's factory firmware the only way the "restore" the ipad without updating to 4.3.1 is to erase all files in the ipad settings, if of course you have previously j/b the ipad you need to have the shsh blob in order to restore the 4.2.1 via itunes