I believe we did a one-question gender microsurvey before (linked to
one of the new-user features?). I don't know whether the data was
useful or not, but I do remember the act of asking the question itself
got some pushback as being invasive/unwelcoming/weirdly
communicated/etc. (and I can certainly symapthise with this)

So as well as the value of the data, we should consider whether the
act/method of asking is going to have knock-on effects on what we're
trying to measure.