Teaching my son his letter sounds

Weve been using this for a couple weeks and my 2.5 year old son still chooses it every morning and is learning! I am very pleased that it has correct letter sounds. I relate to the Montessori understanding of how children learn to read: first they recognize that words are made up of sounds (we did that without an app -- by playing I-spy), then realizing that those sounds are represented by written letters. This app works well for this. I really like how customizable it is, I modified all the settings to create what I wanted.
Suggestions for improvements:
Repeat the letter sound more often while they trace the letter.
Remove the thumbs down frowns when they get it wrong, maybe a question face and a shrug or something, or nothing.
Better graphics -- photos would be best.
I turned off switching between groups of letters until they are mastered, however we cant get back the the first group that he already mastered and it would be nice if we could.
Thank you for the nice app!

Learning with apps about PocketPhonics (basic edition), v2.1