"When using portable CT test sets keep one thing in mind - what are you accomplishing with it??" Great statement. I believe the OP was asking about field testing of large numbers of IT's in a substation environment. What can be done in a practical amount of time is to verify the ratio, polarity, excitation, winding resistance and some kind of test on the secondary insulation (megger, etc)? Additionally, one must balance local safety (lock out, tag out / hold card) rules, environmental conditions, cost, scheduling and available test supply power.
In my world (contractor - utility / heavy industrial commissioning), it is #1 to satisfy the customers specifications / requests, #2 to fulfill my own (trust / distrust) in the (design / application) of the circuit. #3 if there is a problem (most likely in wiring) to identify the problem, have a way to rectify the problem and #4 to document the results in an efficient and meaningful manner.
With all of that said, there are practical limitations to anything that is performed in the field. Additionally, I believe it really depends on what part of the world the work is being performed. The best example would be in what I call the "dead tank" world, meaning the CT's on (outdoor) breakers and transformers are normally located physically within the device itself. I'll pick a power transformer as an example. Unless there are steps taken during the construction of power transformer (halt transformer construction activities so commissioning / relay tech can enter transformer), the only way to test a CT in an assembled power transformer is the voltage method - one is not going to pass power frequency current through a transformer winding to access the CT primary any other way. The voltage method, has been approved in the IEEE C57.13 Field Testing Guide for as long as I can remember IEEE C57.13.1-1981.
Getting back to the OP questions, what is good test equipment and why? What is not so good and why? I believe the Omicron CT Analyzer is the best because it is the lightest and quickest. My company owns a Vanguard EZ CT2000C. I avoid using it because it is slow, heavy and when I have an issue it offers limited control of a manual test. One could argue that the Vanguard (or others using similar test methods) is "better" because it tests excitation tests with "high" voltage and thus is also testing the secondary insulation. As mentioned in the OP, megger tests are often required and I can say that it is much quicker to use a separate megger than the built in megger in the Vanguard (or others). One could also argue that if OSHA (national safety) were on site and witnessed a single person lugging a 73lb test set around by themselves and applying 1200+ Volts @ 1+ amps, there would be some kind of discussion. Given that the equivalent Omicron and Vanguard are roughly the same price, that's my opinion. All of the other modern field CT voltage method test sets are basically the same general design as the Vanguard. My company has had both the AVO/Megger and Adwell versions in the past and they have been abandoned for reliability reasons. I believe it is also important to select a test equipment manufacture that can support the product locally and in the native language that you speak. My second choice would be OMICRON CPC-100, especially if I have other testing in substation. The CPC offers the additional benefit of being able to test via voltage or current method. I made a test box to manually change the taps on a multi ratio CT. Yes CPC is much bigger and heavier, but there are many things it can do, it has automated excitation tests and the reporting is easy. Years ago, I had a Programma Sverker 750. With a few switch boxes and a 1200:120 VT, I could accomplish much of the same (without fancy reports) in a smaller, lighter, less expensive package.
Some years ago, I had an Engineer question the CT Analyzer, as it performs certain tests (excitation) differently. I was provided the attached KEMA report, which passed the scrutiny of the utility protection and metering departments.
