I did the six week then the eight week Mid-Volume plans earlier this summer. I wrote up my impressions on the big Polarised Plans are here thread - https://www.trainerroad.com/forum/t/polarized-training-plans-are-here/55844/389 - I joined the AT closed beta about halfway through that block but chose not to turn it on just to see what the base plan did.
Remember that the 6 week plan is Base and the 8 week is Build. I didn’t find the progression too bad, the only one that caused a problem was going from Deseret to Bartlett Peak and that was because the rest periods became too short for the loop I was doing the workouts on (I did all the workouts outdoors and I live in a very hilly area so it’s a bit of a challenge finding 16min hills with 3min descents).