I am using congress stones with my sharpmaker for more than two years.
I bought five pairs to try different stones: ruby in 150 and 320 grit, moldmaster in 240 grit, flex in 150 and 320 grit. I am using them dry. Ruby and moldmaster works very fast, and I am using them the most. Flex is much slowly, but leaving better finish.
Please, keep in your mind, that these stones were not designed or made for sharpmaker. Some of them will not fit the base, some can be little loose. Out of my 10 stones, one doesn't fit. Moldmaster stones fit very tight, ruby more loose than standard stones (I do not see too much problem here, may be one degree difference).
In general, I am happy with congress stones, they are not expensive and do their job.