Yes, the pre-inspection is necessary.
At least, you should check that TOS series can ensure your safety, such as check that TOS series is properly grounded, or the test lead is free of cracks or tears.
You need to also perform the pre-inspection by shorting between the low-voltage and high-voltage test leads to find that TOS series results in the FAIL status, which also check the operation of TOS series and the status of the test leads.