The Pinpoint Salinity meter will give you what you need. It has the full range and accuracy for TDS reading of 0-1ppm and up to 200,000ppm. 53,000ppm is the equivalent of 35ppt Salinity.
So it's basically a TDS meter with a high end scale? Is it a pocket meter? If it's like the Ph pinpoint then it's mounted in the tank and I can't see how you would be able to check your RO without a lot of work.
There's no reason to mount it to the tank. Salinity doesn't change all that much. Just swirl the probe in whatever water you need to test. You can see if your limewater is saturated with it also.
