It's got nothing at all to do with method, only simple minded remedials like tennet think this way.
I.E.
tennet charges 40 per hour wfp
Trad guy charges 50 per hour
Who's the numpty now? :

You are right about the 10 minute house, no way wfp will be quicker, one big set back that no one ever tells you about is waiting for the drips from the tops to stop hitting the bottom especialy if they are concrete sills.
Be very, very careful who you take advice from, wfp has many issues & IS NOT the magic wand some would bully you into thinking.

Now, anyone else?
Tony