Denver Radon PFE presentation I agree that outside venting is a good idea however the reality is most crews sent out to do two jobs a day or one big job are too time crunched and not willing or in many cases not capable of doing any system diagnostics. So the concept of OSD was to make it super simple and very quick to do with no math, no extra vacuum airflow or pressure measurements or even needing an app. Obviously you can raise the radon levels way up by venting into the basement. At the same time if you are trying to measure a tenth of a pascal or thousand of an inch vacuum an open window and a bit of wind will make that difficult to see. The solution is to minimize test run time by having a super simple set up that allows multiple test variations at the same time test hole vacuum is being measured.
In about 2 minutes you could test the performance of an RP140, RP145, RN3 and RN4-4 fan with equivalent 3" or 4" piping used. And the installers only need to refer to a chart that is small enough to tape to the body of the fan. As for radon exposure people always forget that risk is based on Dose. Dose requires two components - an exposure and time being exposed. 2 pci/l in your house is 2X12X365 = 8760 pCi/l/hrs. which most of us would not consider a serious risk. If you raised the basement to 20 pCi/l for one hour or 40 for 30 minutes that is 20 pCi/l/hrs.