Yes, they work and well. If buying one get one that can read in RMS, in both AC & DC. Otherwise reading many inverters will result in screwy readings.
Ultimately they may not be as completely accurate as your shunts but there is no disconnecting and reconnecting so checks can be made easily, safely , quickly. Also means checks will be made as needed. In most cases if there is a difference between the clamp on and the shunt readings it will not be of signifigance.
If you find a screwy reading with the clamp on then you can go for the shunt accuracy.
My example: I was having trouble with load handling loss with my three Gel Cell batteries. I found the problem one with the clamp on. Load testing individually had not shown the bad battery. I finally set up a load common to all three and monitored the current from each. It showed two batteries current was increasing, one was dropping. As I watched the bad one eventually flipped polarity meaning it had now become a load to the other two. Removed the bad one and got tow more years out of the remaining two units.
If I had to connect and disconnect I likely would have missed the significance. To monitor in real time I would have needed three meters and shunts. With the one clamp meter I could quickly move it around. Of course it wasn't real time but it fast enough and I could see well enough what was happening.
Note: I have my meter because I needed it for work. I did not buy it just for the boat. Can measure up to 1,000A so that should enter into your decision but since I bought mine they have come down a lot in price and also there are more of them available. Klien Tools makes one that should be suitable for you with a much reduced current capacity which keeps the price down. Also available at Home Depot.
http://www.amazon.com/Klein-Tools-CL2000-Clamp-Meter/dp/B003LH7NH2
