Just get yourself a good quality pin type meter. Accuracy shouldnt be an issue (interested to know why your not "convinced"). Test and retest the same cleft dried to the optimum content from a supplier you trust. That, along with the weight will give you a good baseline. If the results are quite close/identical then your good to go. Test each of your clefts in the exact same way and theres no reason you cant have an accurate measure of moister for each of your clefts. Once you reach that or your own desired moisture level id machine the clefts to identical dimensions and then youll be able to weigh them again to get an indication of density between clefts.
I'm sure you're right that there are better and worse meters out there. The ones I've seen are simple, and use small pin probes to take readings from the outside of the cleft. I just wonder how accurate and consistent they can be when it comes to green clefts, considering the length and thickness of the pieces.
Anyway, as an amateur, I don't have a meter - good or bad! At this stage of production when the clefts are completely wet, I prefer my method, as using maths gives me very tight control over the drying process. The volume of the cleft doesn't change, so by using mass and calculating density I can see very clearly how things are progressing.
For example, my cleft #6. When I laid it down on 27th Feb it had a mass of 6005g and density of 0.7 g/cm3. On the 10th March, the mass was down to 5504g, density to 0.64 g/cm3. The target density is 0.4 g/cm3, which means that I can calculate the target mass at 3557g. All I have to do is keep checking the clefts and noting how they get lighter, until they reach my exact target. If I can find a kiln this method will also make it easy to study the comparative drying rates.