I haven't used either of those suppliers, but I recently bought a car satnav from handtec (www.handtec.co.uk), who were very efficient and delivered next day with no problems at all. They have the Garmin Etrex Legend CX for £179.97.
Just back from doing the Torres del Paine circuit (well almost) - Can definitely recommend the full circuit (rather than just the W) as the back half is much quieter, and the view of Glacier Gray when you cross the John Gardener pass is truly awesome. Weather is very varied, sun, wind, cloud, rain.
Unfortunately a huge forest fire broke out (apparently caused by a czech camper tipping over his stove) which has destroyed some 30,000 acres and resulted in the entrance to the park being closed when we were one hour from completing the circuit. We had to turn back. So after circling the torres for eight days I have yet to actually see them !