The CT-5 and CT-4 I think are significantly different. Be careful. In fact the CL-4 and CT-4 are closer to each other but the CT-4 has high voltage sync and the CL-4 has low voltage sync. The CT-5 also has high voltage sync but it has LED digital displays instead of the dial only on the CT-4.
Only the CT-1 up to serial number 533.999 has a high voltage sensing circuit, i.e. CT-1s with serial numbers from 534.000 on can be safely used with any camera as well as all CT-3, CT-4, and CT-5 models. The CL models have a LED instead of a light bulb for signaling readiness. The CT-5 has no manual mode, though.