I will add my 2 cents as people are posting their experience. Around 8 months ago I started this method, it was pretty hot still at that point and paces were difficult. I also changed the method from what sirpoc posted, did a so called x factor session. Honestly, I did too much and blamed the system. You have to be very, very careful adding in the x factor element and need to know what you are doing.
My results were very disappointing and all but abandoned the method over the dark months of winter. Stumbled back across the thread and saw the progress of sirpoc and decided to start back up. What stuck me as I am around the same age as him and likely way more talented, but he would beat me in a race. Just didn't seem right. For instance, I could probably run 15 miles a week from zero fitness and break 19 in a few months which he struggled to do for a long, long time.
Anyway, second version of trying this and have just run the schedule laid out almost as a carbon copy.
Things I have seen most people doing, myself included, getting wrong are:
1. Not adjusting for heat and hills
2. Too much x factor work or an obsessions with the 5k work still as your x factor. If you are going to do it, it should be a sprinkling and very , very hard. But, ultimately, if you use it, you are wasting a load increasing sub threshold session. It's all about accumulation of load again, again and again.
3. Seems to have been overlooked. But don't do too much . Get the balance right. I see some guys doing one session a week way too long and then saying it's not working, or 3 sessions a week as laid out but way too much in terms of the easy/sub threshold balance. This 75/25 rule sirpoc has said about seems very straightforward, I've heard others mention it but seems to really be that nice sweetspot.
4. People are expecting miracles. You don't over even 2-3 months. Maybe 6 you will really, really notice the difference.
5. It's very very hard for talented runners I think in particular to adapt to this. It flies in the face of everything fast guys and girls are told and have been coached. To do the same thing, week in, week out no matter what the time of HR year is very alien.