Letter Sounds™ 1 Pro and Letter Sounds™ 2 Pro are different apps!
The key difference between the 2 apps is that Letter Sounds 1 Pro targets basic letter-sound knowledge (single letter sounds), and Letter Sounds™ 2 Pro targets longer letter-sound knowledge (two or more letters such as 'igh' like in 'light' and 'sh' like in 'ship').
Letter Sounds™ 1 Pro is designed for learners who are beginner readers, and Letter Sounds™ 2 Pro is more suited for intermediate level readers (i.e., students who have already learned basic letter sounds). Both apps are suitable for older readers who are experiencing reading difficulties.
More information about the apps can be found here:
Letter Sound™ 1 Pro: http://www.readingdoctor.com.au/letter-sounds-1-pro/
Letter Sound™ 2 Pro:http://www.readingdoctor.com.au/letter-sounds-2-pro/