You need use ST42 more and get to know them better. 
In what sense?
I know they are pretty accurate, but I find the ergonomics aren't all that great for measuring larger parts. A good example is if you are measuring in-circuit and balancing a PCB attached by cables to a chassis. I'd find tweezers difficult to hold let alone read in that situation, and why I rarely measure in-circuit anyway.
Just for reference, attached is a photo of a quick comparison of measuring a 330uF 16V SMD electrolytic with my CKT bench LCR, the Peak atlas ESR70+, and the Shannon Tweezers ST42.
CKT5000: 297uF 330mohm
ESR70+: 306uF 200mohm
ST42: 298uF 341mohm
(edited to fix typo in labels)
The ESR70+ reads ESR a bit low, but that is because it measures at 100kHz whereas the others are set to measure at 100Hz (more appropriate for some random electro).
The CKT5000 and ST42 are set for 100mV test voltage. The ESR70 uses about 80mV (+/-40mV). I didn't check, but I think those are all Vpp (and the manuals don't clarify).
Further tests...
ST42 set for 10kHz reads: 217uF 223mohm ... hmmm?
CKT5000 set for 10kHz reads: 297uF 203mohm
CKT5000 set for 100kHz gives invalid reading: -17uF 189mohm <- this is a good example of where knowing the instrument is important
ESR70 Gold measures at 50kHz which might be better for accurate ESR on a bigger electro than 100kHz of the ESR70+. I just want to know order of magnitude to know if a cap deserves replacement. I am not using it for precision ESR measurement, because for that I'd use the bench LCR and a proper hands off test fixture.
BTW, the CKT5000 is using correction data for my SMD test fixture where I was last measuring single digit pF 0402 capacitors.