I had one on my Chartplotter/Fishfinder and it still got jacked! Thief cut the 1/8" steel bracket and stole the lock with the unit. The lock did not fail. Good news is that insurance covered the loss (less deductible). The fact that there was clear evidence that the property had been forcibly removed and was secured to the boat was a critical factor in having the loss covered. That being said I will buy another to use with my new unit, but remove electronics (which requires a hex head wrench instead of just thumbscrews) from boat for overnight periods. For short forays away from your boat it is a great deterrent.
The lock was easy to install, but it didn't fit my Lowrance Disc 8 VHF radio. The outer shell didn't fit within the radio bracket. I could mount the inner shell, but when I tried to slide the outer shell with the lock it interfered with the side of the mounting bracket preventing the outer shell from sliding fully over the inner to lock. They provided several screws and hardware for the different models. My boat is small, 22', so there isn't very much space for electronics. This should work fine on a large boat with plenty of room.