I chanced upon a Sofirn SP31v2.0 "no stepdown version" from Sofirnlight.com website.
Ordered it last May, but shipping took a long time, and arrived this September (nearly 4 months).
It doesn't seem to be listed anymore (when I ordered it, I think the site indicated there were 3 units left only)
Anyway, decided to compare the first few minutes to check how it compares to the regular SP31v2.0
(I don't have an integrating light tube, so just shone the flashlight on the ceiling of a small room, and used zak.wilson's 'ceilingbounce' app to record the first 10 minutes 'runtime' graph)
Tested a regular SP31v2.0 first:
(it steps down to around 50% brightness after 3 minutes and stays fairly constant brightness after that)
The SP31v2.0 "no stepdown version" does appear to have no stepdown, but brightness likely tracks the battery voltage:
