I had 2 of these, both from new, returning the first for the second. Both of them exhibited the same fault - namely they hang / freeze during use. They hang at random points, any time from switch-on to several hours later, so very unpredictable and very unreliable.
They hung / froze regardless of battery type, or whether the Micro SD card was plugged or not.
I updated the software in each of them to the latest - v2.6. No difference.
I can only conclude that there's a bad batch or design problem. Either way, Garmin are not admitting to it.
If it weren't for this, it would be a great unit. Colour screen, Hi-sensitivity receiver - which seems to work better than the standard ones. Not sure about the joystick, though it's easier to use with gloved-fingers that the buttons on the side. Trouble is, you have to use those too to navigate round the screens.
You can get it to save tracks to the MicroSD card (not supplied), but once on there, the unit can make no further use of them. I never quite figured out at what point the track got saved to the MicroSD card as the thing never kept going for long enough
One further point - the Vista HCx connects to your computer by USB cable (at both ends. ignore the oft-seen need for a serial to USB cable). If you're using Fugawi, Memory Map, etc, map sure your version can talk to a GPS receiver via USB. Upgrading the software (and OS maps) is around the same price as buying the GPS.
You can buy MicroSD card maps to plug in to the GPS, but not with OS map data, only Topo-something or other, which don't provide the same level of detail.
In the US, the units come complete with with a MicroSD card, either for Europe or for US. These maps are pretty rudimentary, though they have major roads and towns on them (including parts of Bristol like Hanham, Filton, Southmead, etc). Buy one in the UK, and you get squat despite paying almost twice the US price.
In the end, the second unit went back in disgust, too. I'll live with my old eTrex Summit for a while longer.