> Trying to use a Surface keyboard on my lap on a train sounds awkward, the trains I use don't have tables
It's actually not that bad at all, believe it or not. I use the Pro 4 on my lap all the time. The Surface Book does not work in your lap based on what I have seen, but the Pro does fine.
I think my error rate is a bit higher than when using a real keyboard, but the alternative would be not being productive during that time at all. I'm an old duffer though, I remember using CPM machines, 5.25" floppy drives, line editors and dot matrix printers. An iPad is fresh air and clear blue skies compared to stuff I've had to work with back in the day.