The Skymap 3C is a very nice product. They have been making it for donkeys years.
Drawback #1 is no internal batteries. You have to connect it to the aircraft power. I believe it runs from either 12V or 24V systems; in reality this is 14V/28V. My Skymap 2 runs off both. And if it is to serve as a navaid in case of an electrical failure in the plane (pretty desirable IMHO) then you are looking at a substantial external battery pack; of the order of 1" x 6" x 4" (sealed lead-acid) to run this unit for say 5 hours. Easy for an electronic engineer
to construct but a major hassle otherwise. The standard plug-in cigar lighter connector is also flimsy, as I know too well from charging various gadgets from the plane's ccigar lighter socket, and the most brief disconnection will clobber the GPS until it restarts, re-acquires, etc.
Drawback #2 is no internal GPS aerial. Actually this is not an issue since nobody should use a GPS (other than in an open cockpit with no roof) unless they have a remote aerial, either on the roof or stuck to the top of the window. With the Skymap 2 I used the supplied remote aerial, with the suction pad attachment to the window.
Skyforce/Honeywell charge about £100 for a database update, which isn't too bad.
Curiously, from a conversation I once had with an instructor who was looking for work in Africa, no doubt carrying "interesting" cargo
this was the only GPS on the market whose (he claimed)
VFR database included Africa.
Personally, given the close price, I would buy the Avmap EKP IV. The display quality of the Skymap doesn't even begin to compare with the Avmap, for example.