You can adjust the size of the fonts on the Vista HCX. You can really make the data on the trip computer screen really large easy to be seen. But as with any handheld GPS unit, map screens are small to look at.
The 76Cx and 60Cx Garmin series are larger and should be easier for you if you want to go that route. The software is almost identical to the Vista HCx.
small data fields
big data fields