I bought a Memory Map GPS - nearly a very costly error. The thing was hopeless. Bug-ridden and very badly tested, failed on me several times in the first few days of use - suggested remedy from their customer services was to carry a paperclip to insert in the "reset" hole. Not an act of war on a hill in bad weather I suggest ?
...anyway, TISO were kind enough to accept that the thing was pants and gave me a full refund which I spent on a Garmin Oregon 450. Now that is a work of art. Absolute perfection as far as my uses ( walking and 4x4 nav) are concerned. It actually does the whole "car satnav" thing, turn by turn, but using the OS 1:50k as a basemap when you set it to "navigate on road" - as well as all the stuff I need for the hills. I've also loaded Garmins Eastern Europe mapping ( £39 and cover about 6 countries !) for my trips to Poland, takes me right onto the location, even covers all the farm tracks - "follow unpaved road to..." Superb, given that the last location was a hilltop 5 miles from the Ukrainian border.
I now use MM software on my PC to plot UK routes, flag waypoints etc etc then download them to the Garmin and backload my actual track. Works a treat - but I'd not use MM hardware under any circumstance. ( Oh - and they blocked me from their Forum for telling people about the problems I'd had with the kit. Nice.)
Edited to add.... in terms of Tims original post, I'd not put it past MM not to have tested the software properly - likely scenario, nor to be looking for a way to get folk to buy all their maps again - cynical scenario.