I discussed the problems with RU in the darolutamide thread, and in the link above to the strength comparison with daro, but in short the primary problem with RU is likely its short half life.
It has an antiandrogenic strength roughly equivalent to flutamide (which is a reasonably strong antiandrogen, used commonly in prostate cancer and other conditions, though nowhere near as strong as daro). However, RU has a serum half life of only 1 hour, and this likely corresponds to a scalp half life of around 3-5 hours.
Therefore it really needs to be applied twice a day to be effective. It also would need to be applied in HIGH doses (5-10%) on each application, to make up for the fact that 3-5 hours later, only half the RU you applied might still be there.
When you start doing that, the systemic absorption actually becomes considerable and it's not so clean a drug. I maintained for one year on 5% RU and 5% minoxidil twice daily but when I cut the dose of RU and dropped the minoxidil I lost hair. I went up to 7.5% RU until I got on daro, and once I stopped the RU, I definitely felt better overall, so there were some side effects creeping in at that high of a dose.
At 2 mL twice daily of RU 7.5%, you're getting a daily exposure of 300 mg RU, which is actually a very high dose when it absorbs systemically. And it costs a fortune. And the levels are bouncing up and down like a yoyo all day.
Overall not an ideal treatment. If you want to talk about theoretical "not for human use" unlicensed Chinese factory topical hair loss compounds, darolutamide is superior to RU in almost every way.