Yes. Perhaps it's not as reliable as recalling every SDS200 with a serial below xxxxx and replacing the display module or removing all the solder mask around the screw holes, but it works in the majority of cases.
I could ask you the same.
If the majority of SDS200 units had the RFI in the audio problem, the odds of people buying multiple units and getting all good ones would be vanishingly small. Let's say that 90% of SDS200s had the noise problem. If you buy one, your odds of getting a good one are 10%. If you buy two, the odds of both being good are 1% (10% of 10%). And if you buy 6, your odds of getting all good ones drop to 0.0001%. There are a couple of posters who have 6 or more SDS200s, and no defective units, so that's pretty solid evidence that the defect rate is a lot lower than 90%. If the defect rate was 50%, the odds of buying 6 good ones are still only 1.5625%. You can estimate a reasonable upper bound to the defect rate D by working out what value of D satisfies the condition (1-D)^6 > 25%.
There's also the "squeaky wheel" factor; people with problems are more motivated to post than people who don't. So even if the "my unit is bad" and my unit is good" posts are about equal, you can't presume half of all units are defective from that.