Yes, I have one that I've used with some success. I read an article on the agromax website that had some suggestions for timing. I ran mine in 15min increments in the middle of the lights on period for a total of 2 hours combined UV "on."
I've not seen at research to know if the incremental approach or all at once is more effective. I also haven't grown enough plants consistently to test it myself. I could not say for certain that it helps but it did not hurt anything either. I did have a gnat issue and the uv blast killed them pretty quickly.
So, I think using it towards the end of flowering can only help. Especially during a critical time for developing mold or fungus issues, the uv may help keep that at bay.
I've not seen at research to know if the incremental approach or all at once is more effective. I also haven't grown enough plants consistently to test it myself. I could not say for certain that it helps but it did not hurt anything either. I did have a gnat issue and the uv blast killed them pretty quickly.
So, I think using it towards the end of flowering can only help. Especially during a critical time for developing mold or fungus issues, the uv may help keep that at bay.