I tried it this year. Not on track, but on a bit of road, same every time. I chose a slight uphill to not risk injury.
Improved some, but leveled off too soon I think. I may have been a little too tired on the reps since I normally did workouts the day before
#1 2@30.5s
#2 3@29s
#3 4@29.2s
#4 4@28.65s
#5 3@28.75s
5 weeks skipped
#6 2@28.6s
3 weeks skipped
#7 5x30s sprints as maintenance on holiday
4 weeks skipped
#8 4@28.7s
2 months skipped
#9 3@28.95s
I have stopped at 4 since 5 starts to cost some in recovery to the next day and I did this in addition to workouts.
In addition I am better at using 5x10s hill sprints, consistently without breaks. often 2 times a week.
But one can gain a good improvement fast and maintain that without too much effort. I feel much better at the end of hard running and at least feel I have more power in the kick. Definately this running is good for my top end speed running form. I may have the main problem there.