Very common issue - with some people it is impossible to change.....
Extra space inside the build with thinner walls is the biggest seller of boards at the moment (oh - and you cannot get blocks....)
impact resistance is the same (strangely, soft body impact with aquapanel and blocks is the same when you build it right) but easier to repair with boards - hit it hard enough it will break!
When they tap it..... ask them what their roof is being made of!? the roof tile is the same as a boarded wall, and has rain and hail rattle off it (so many builds have room in roofs as well now)
I will happily talk to potential clients for you steve!