Track IR 4 or Track IR 5

I have a personal dilema. Should I go for TIR4 or 5.
TIR4 is cheaper but does the extra $30 justify to purchase the more recent TIR5
What are the differences between the two?
TIR4 is cheaper but does the extra $30 justify to purchase the more recent TIR5
What are the differences between the two?