I have one of these and have been very happy with it (it came with the boat so I had no choice)

. The display is visible on the brightest day and the resolution is decent on the graphics side. The most recent system update (v1.6.0) works well (maximised detail read from the Navionics pack). I have the Navionics Gold No. 28 British Isles map installed on the unit. The wreck locations marked on the charts can be very handy.

The maps that ship internally aren't very good for detail round these parts so you will have to invest in a chart pack (bear in mind that this will set you back an additional 160 quid on top of the GPS cost of GBP300!).
On the down side the unit does drop position the very odd time (usually in the west channel at the entrance of Cork Harbour which has high cliffs on the East and West approaches). This can be dis-concerting but not a problem if you know the general lay of the water where you're at. The other thing that I have found with the unit was that the map pack can loosen in the SD card port and it'll lose the map data and fail back to the internal Lowrance map data. A bit of folded newspaper keeps this under control though so it's not a big deal. I can't seem to get the unit to talk to the DSC radio but I think that the radios fault to be honest.
I must say I find it very good on the whole.
Phil