I am the administrator of several DNA Projects at Family Tree DNA.
Today I was looking at some of the statistics of each of the projects and noticed quite a few members in each project have taken various portions of Mt-DNA but only about half of those testers have taken the Full Sequence test which covers all the Mt-DNA that can be tested.
Below I have placed a table describing what genealogical benefit a tester will derive from each test.
If you have taken only the HVR-I or the HVR-1 and HVR-2 which FTDNA calls Mt-DNA Plus you might consider taking the plunge to the FULL SEQUENCE Mt-DNA test.
The cost of the Mt-DNA Plus is $79 and the price of the Full Sequence is $199. If you have already taken the $79 test, you can upgrade to the Full Sequence for $139. This post is being written during the Christmas season and I have coupons which expire the end of each week through December 31, 2016
If you would like to read more about FTDNA Mt-DNA testing go to the Learning Center at https://www.familytreedna.com/learn/dna-basics/mtdna/