There's still lags in the UI, regardless reduce transparency mode is enabled or not.
That said it fixed quite a few things from beta 8 that I reported : buttons on lockscreen or photo viewer, folder look, unsure but my third party keyboard seem better integrated. Magnifier loop to place the cursor is again transparent even in reduced transparency mode.
But some bugs are just not fixed. For example searching "transparency" in settings brings nothing, quite bad for an **accessibility** setting in my opinion.
I haven't tested yet on beta 9, but on previous using safari (as a passenger) while waze is running on carplay could crash carplay, and public hotshot.