I retrofitted one to my Automatic 2003 mini one. I bought the rev counter with mount and wiring harness off of eBay for about £30. It took about an hour to install as you need to pull the speedo out etc but was not difficult. When installed you will need to have it turned on. I bought the cable and software off of eBay for about £30 (you can also run diag and do all sorts of other things like key programming and retrofitting etc).
To be honest all in all, not a difficult job if you have all the bits you need mand looks great!
Hope that helps!