Thanks very much Dan & Justin. Very sorry for the delay in my response, I expected I would receive an email from iFixit if there had been a reply. The performance of the Samsung looks way better - I will be going for that one.
This weekend’s work sorted, clean install of MacOS and we should have a much faster computer.
Do you think that this SSD would work OK? I would be good to know which SSD HDD would work in this way? Do they all just use the same power etc? https://www.amazon.co.uk/Seagate-BarraCu...