What has been relayed to me is that the openings are rarely a standardised size so the door sets won’t match. I’m referring to older properties where I suspect most of the work will be done.
Surveying work isn’t the issue, it’s more you won’t find off the shelf door sets to fit the openings and so altering frames and doors is nearly always necessary.
That would mean having some kind of workshop to carry out alterations which I was hoping to avoid.