I have used both the coopers and muntons drops with good results... as well as cane sugar and corn sugar.
I liked the Muntons tablets due to the ability to more reliably set the carbonation compared to Coopers (the coopers drops seem to have a high degree of variability in size in my opinion), however, I admit, that I did not find any noticeable difference between bottles of beer carbed by Coopers Tabs.
I did not have the flake issue you had with the Muntons.... just curious.... how long did you leave the bottles to carbonate? Also, what kind of beer was it? I have used the Muntons on Vienna Lagers, Cream Ales, and I think a couple Alt beers without any issues.