Wow, okay so the plugin didn't work so good when I first installed it but the support from the plugin author is fantastic. Having attempted to troubleshoot the problem myself I eventually conceded defeat and posted my problem to the plugin forum. Turn's out that there was a small issue with the plugin but within a few hours the author had it updated and fixed.
Woohoo, Register Plus Redux is now working exactly as I would expect.
One reason why I wouldn't rate this plug as five star is for the lack of documentation for custom CSS styling. I'm a complete beginner when it comes for CSS - I have to have my 'For Dummies' book to hand for the simplest of tasks - so I didn't have a clue how to alter the styling. In fact I've turned to simply digging into the PHP file to make some minor adjustments.