'tis fiddly, I normally strip back an inch and half of sleeve, sort the
wires then trim to length, damn sight easier than trying to push/pull th e sleeve and sort 1/2" long wires.
Bear in mind the £10 ones only test at DC, they won't pick up a badly
pinched or kinked cable or other weirdness that can screw up the actual
data transmission. Still useful to detect gross DC errors like open/shor t wires, phase reverse pairs, crossed pairs etc.