I'm considering buying a GPS unit. What I'd really like is a rugged hand-held device with OS 1:25K full-colour mapping. However, my preliminary reseach suggests that such a device is not available at least as an off-the-peg item. Even the mid-range units (such as the Garmin Vista) that purport to support mapping don't do proper OS mapping. They don't seem to be worth the extra money over an entry-level model.
One option for a high-feature system seems to be to use a PDA with either a plug-in or a bluetooth GPS add-on. This sounds attractive in that it the PDA fulfils other roles too (diary, etc). Does anyone have any experience of such a combo or any other recommendations? Can the bluetooth GPS unit stay in a backpack so that only the PDA needs to be hand-held?