Week 4 finished, have a niggling pain in my right calf after R2, but don't think it is injury as such, as I can massage it away for a while with a roller.
Looking forward to week 5, 20 mins in run 3 seems like a big step, but only one way to find out.
Definitely seeing the benefits, I'm running further in the 3 week 4 runs for the same times, but my heart rate not going quite as high at the end of the longer sections.