The /f switch only works while booted in Windows. That will set the test for the next startup when used at the Run prompt. The entry at the accessories>command prompt will see the same thing there.
The /r is used at the recovery console since the /f switch won't work. Either way the manufacturer's tools are a bit more thorough with the diagnostics as a rule. If the drive is going on you you'll want to know now in order to still be able to retrieve all your files off of it once you have a replacement in rather then waiting for it to fail completely.
I bailed one friend out where he had some 1,000 family photos on a drive where the larger storage drive then saw Windows put on that fast until I could slave the first for recovery. If he had kept running it he would have lost everything. The drive tests will show if it is the drive without delay while you still have time there.