I used these flash heads 35 years ago and acquired a faulty kit at low cost in 2017. One head is still working. With a full power flash duration of 1/400s despite a small flash tube, they have a fairly level output curve. Tests were made using a Godox X1-TS wireless trigger hard PC-wired to the flash, Sony A7RII with 55mm f/1.8 CZ lens, at shutter speeds from 1/160s to 1/8000s using my painted desk fan test target.