The advantage of parkrun is that it is a consistent course, so great for benchmarking. And unless you are troubling the 16 minute mark, there will be people who are faster than you, and just as keen not to be beaten. It's as much a race as anything else, despite the branding Or, rather, it's a race for those that want it to be.
I use parkrun for benchmarks/fitness tests. The only issue I have is that the courses aren't very flat. The nearest fastest one means a trek over to Huddersfield (a 20 minute run there is "slower" than a 20:45 run at Halifax, and a 20:30 run at Bradford).
My parkruns ranked in order of how good they are:
1. Halifax parkrun 00:20:45
2. Bradford parkrun 00:20:42
3. Huddersfield parkrun 00:20:00
4. Woodhouse Moor parkrun 00:19:57
Never raced/been fit at these two
Horton Park parkrun 00:24:07
Skipton parkrun 00:28:38
I think the Halifax one is by far the best, would have been 20:30 at Bradford, and 19:40-45 at huddersfield/Woodhouse.