I'd never really considered the benefits of a field monitor before but decided about half a year ago to get one. I went with a Lilliput 665GL monitor to go with my HDMI camera and I must admit that it's been a real benefit to my landscape photos. Being able to use a 7" monitor instead of the view finder gives a much better idea of the quality of the picture at the time of taking.
But that is a review for another day
I just dipped my toes in the water again for another monitor, this time the Lilliput 5dii/O/P. Again I'm really impressed. There is a lot of improvement on the 665 which I think this is a spiritual successor to. For one they have coated it with a new rubberised coating which makes it reasonably water resistant and a little bit tougher than the 665. It uses external battery plates which mean that I can take it for walks and just carry a few extra cells. Oddly enough it doesn't use the Canon batteries but I had a few Sony camcorder batteries that fitted nicely. Battery life is good - about 3-4 hours per battery. Enough to last a good shooting session.
All in all I'm impressed. Now I just hope that it will work on the 5d Mark 3