As far as I am aware, the UT502 utilises the same build as the 501, it just has a different voltage output range up to 2500V instead of the 1000V of the 501. It has the same style latching button for the on/off. It never bothers me personally as all my insulation testing is time based, at least 10 seconds, usually a lot more. You do get DAR and PI ratio tests, but these are for motor windings and not applicable to cable testing.
In comparison to the VC60B+, probably the same build quality as the WinsPEAK. It does have a case with it and a hard front cover that clips to the front of the meter. It did have higher short circuit current than the VC60B+. Probably not as accurate in terms of insulation resistance readings, but it will read up to 5.5 GOhm, whereas the VC60B+ reads up to 2 GOhm.
If you do have earth leakage, you will measure it as a standard 50/60Hz signal. In an ideal circuit you should not be able to measure anything as there will not be any leakage. If there is nothing connected but the wiring and you are getting mA leakage on a single circuit, then you would need to investigate more. As you add in more circuits to the test, the leakage can start to increase.
It will be dependent upon your actual physical setup. If this is a straight pipe, then the only cable damage you tend to see is caused where the cable is entering the pipe. You may see shavings of PVC insulation around the pipe entry that would give you an idea the cable has been damaged. The pipe entry should be smoothed and may have a bushing installed to protect the cable as it is pulled in. If this is not the case, then again, it would be more indicative of damage to the cable.
If it is a straight run and easy to pull the cable through, then you could just attach a draw wire/string at one end of the cable and pull it all out for a physical inspection. If it is ok, just pull it back in, if not arrange for replacement.
If it is a long run with bends in the pipe, then it is easier to damage the cable. The damage could also be caused pulling the cable around the bends, if the bends are pipe bends, then less likely, if they are actual pre-manufactured bends, then damage can occur if the pipe ends are not cleaned.