Awhile ago I posted about purchasing the Exelys Breakmaster http://3jack.blogspot.com/2008/11/exelys-breakmaster.html
Here's something I ready over at http://www.lynnblakegolf.com/ forum from LGB contributor 'Overkill', a PGA Tour caddy.
I have both and I have used both. However, I like the 'Green reader' developed by HS. It is larger, much heavier and I believe gives a very true read. The Ex is much quicker and is used by a great many caddies. However, it is small, very light and can easily be affected by ball or spike marks. If I do not have a lot of time I use the Ex but I place in on top of a putting disc which gives it some stability.
My basic chart is taking a reading every 5 paces front to back about 4 paces from the edges and one every 5 paces down the middle. I then role the slopes and roll areas where pins have been in the past looking for anomolies.
As you have indicated, the pros can putt////where I have found my work comes in handy is where the green looks to be flat, they are never flat//
If I can help my player with one putt a round, I feel the work has been all worth while.
The green reader "developed by HS" is basically a bubble level style of green reader developed by Padraig Harrington's putting coach, Harold Swash (pic below)
I have noticed that with using the Breakmaster, *some* of the reads are a bit confusing. I usually will measure the Exelys Breakmaster in an "around the clock" fashion around the hole and occasionally the measurements don't make sense...and Overkill explains it. However, I've found that if you *lightly* press down on the Breakmaster, the measurements are corrected.
I am a bit surprised that Overkill does use the bubble level green reader since the Breakmaster gives you a great digital readout of not only where the slope goes, but how much it slopes.