Explorist 500 questions

I have an option to buy an Explorist 500 form a friend who has found it does
not suit his needs. After much searching I am questioning whether it will
suit my needs too. Maybe someone here can help:

1. I will definitiely be using it in the Lake District in the UK in October
for hiking. I have read that the Magellan Topo maps are not very good for
the UK, is this correct? Is it possible to manipulate another brand of map?

2. I use a Macbook when on the road and would need to be able to manage my
routes on the mac for ease. I have read there is no way to transfer these
wapoints with the Magellan. Is this true? Also is there any mapping software
(such as Memory Map) available for the mac so that I can plan my routes, and
then use one of the "free" waypoint programs to put this into the unit?
(experience/advice would be useful here - and no I dont want run Windows on
paralells, my HDD gets full of movies/pictures when I am out and about).

Thanks for any help you can offer

P.