Agree with @dakotacraig on the handheld ones. The built-in ones fail so hard and you can't even swap batteries. A cheap handheld meter is way more reliable and you can use it for other stuff too. It just makes more sense than trusting a part that's known to break.

Give Grease Cleaning Pros a call. Their prices are super affordable compared to the corporate guys, and they do a much better job cleaning the baffles.