Well.... 8% per year = 40% in 5 years going by simple interest & closer to 60% as per compound.... Plus being locked in with the same provider for 5+ years -- not sure if that is a great idea.
Having said that the so called price protection is there & also the hassle of tracking & paying monthly is avoided... So, if you want to avoid the later, you can consider going for it
Personally would always go for 1 year recharge... and get 1-2 months (or whatever is on offer) for free..
Just to add more to the calculation (I mean confusion), you will be actually paying out 20% in a year for actual bill payments monthly. So averaging out 8% of 100% in 1st year, 8% of 80% in 2nd year, 60% in 3rd year... so you will probably end up getting closer to 25% in banks and not 40-60%... so basically I feel its not much of a difference