Haven't read the full thread but just giving my side of things.
Took a mortgage out with them in 2017. Got approval in principal letter within 1 week. Solicitor did mention they requested a lot of paperwork but only took couple of weeks to draw down the loan. They have a great variable rate and great overpayment options.
I made sure that all my accounts were 100% for 12months and gave them a printed folder with something like 13 dividers so they had every last bit of paper work they needed. I'm also self employed so that included company accounts and tax clearance certs etc.
Not trying to take away from other posters and I'm sure they can be hard work to deal with but if you dot the I's and have everything 100% right then you shouldn't have too many problems.