Mobile Safari is a bit of a pain for frontend developement. There's the javascript-based FireBug but it's a far cry from the real thing or the Chrome developer tools.
Of course, you don't need to do it all day every day - you can use your laptop for frontend work and an iPad for backend development in the park on nice days.
Thanks, definitely going to give it a go for backend development. It might actually be quite nice to have some forced segmentation between backend and frontend work to avoid getting distracted by the design at the wrong times.
Do you have many problems with sunlight on the screen/ glare?
Of course, you don't need to do it all day every day - you can use your laptop for frontend work and an iPad for backend development in the park on nice days.