I have owned 2 Original Mini's, a Mini 2.1, a Woodvil Mini and a18490 Woodvil. I sold them all because I prefer the Grand.
My memories of these are; The 18490 lasted longer and slightly out preformed the 14500. Also, the Original Mini 2.1 accommodated the RM2. The original Mini did not, I had to request a special one from Rob to fit the 14500 mini. These were made a year to three years ago, you should email Rob to inquire what changes have been made to the newer Mini's and Mini 2.1's.
On an overnight run, I would have to take several spare batteries for each, the mini and the 2.1. The battery and bottle size of the Grand was way more convenient for me personally.