The GPS devices with marine mapping to my mind are a massive advance in useful tech for smallcraft where a mahogany chart table and rack of paper charts is out of the question. The only proviso is not to use them without the backup of understanding basic navigation and what to do if the GPS fails. I print out and laminate charts in A4 size for areas I will be visiting and carry a decent compass as my backup but these never really come out of the bag from year to year.
Have a look at this thread of mine from 2015 when I upgraded from a handheld to a larger screen demountable unit that fixes to the seat...
http://www.rib.net/forum/f37/garmin-...tec-69858.html
The handheld had served me well for many years but the 45DV has proved even better.
You mention depth, the handhelds of course show the expected depth on the maps but the larger unit has a transom mounted transducer hence shows actual depth under the boat.
On a smallcraft it isn't essential to have real time depths shown but I come from a background of larger craft (i.e. sleep aboard types) where the depth sounder was a useful navigation (and keel saving) aid so I do feel reassured to have that facility now.
Here is the current version of mine...
Chartplotters: Garmin Echomap CHIRP 45cv (dv) Excluding Transducer (010-01565-10)
Note it comes without a depth transducer which is about £60 extra but the charts for all of UK are included so it's ready to go as a mapping GPS unit.
I run mine from a 7AH battery.
If you do decide on a handheld then this Garmin with charts included is something of a bargain at £215...
http://www.marinesuperstore.com/gps-...d-bluechart-g2
Beware if buying a handheld without mapping pre-loaded as the Garmin Bluechart software for the UK is about £200. That's why the Garmin 45 is such good value as with the charts free the unit is effectively only £50. There are of course ways round the cost of genuine charts but that is a personal decision.