I have a couple of thoughts on this after having purchased a keggle with valve and thermometer built into it (NOTE: I use it for my mash ton).
1. The thermometer was positioned right above the valve, I dam near melted the thing while I had a flame under the keggle. I have since pulled it and replaced with a $16 Wallmart wireless thermometer. I also spot check with another thermometer to be sure my mash is evenly heated and I'm getting correct readings.
2. The valve, like the thermometer also has issues when I have the flame on high. The valve handle, which has a rubber coating, tends to melt fairly easily. I've played with the flame (using a banjo burner) but have a hard time. I believe this problem can be solved by getting the burner closer to the bottom of the keggle. The banjo burner currently sits about 7-8 inches below the bottom of the keggle... lots of heat loss. The other option would be to extend the valve out further from the side of the keggle so that it is not under or close to the direct heat.
Like others have said, the valve is far more valuable to me than the thermometer. If I could do it over again, I would have skipped the thermometer.