Bumping for you as I want some recommendations of suppliers of this.
I used it years ago and it was fantastic (but can't remember who I got it from). It was hard wearing and did work when lights were on. Can't remember if it reduced daylight that much. We had it on a kitchen window that was about a metre from our neighbour's kitchen window and it was a very dark spot anyway.
I have Purlfrost. I think there you can do it more cheaply it you just want something opaque, but I wanted a pattern. Light not a problem, but not really effective with the lights on, much like net curtains. At least I think that's the case, but can't remember if I have checked this or just assumed. Can get husband to undress in the window with the lights on when it gets dark later and go out and check if you like.
Not very helpful as the stuff I have in the kitchen is discontinued, but;
It reduces light more than a naked window, but less than nets (well, the nets I used before anyway)
It works with the light on (I went outside to check the first night)
It's pretty hard wearing except when you have a cat trying to catch a fly (I have five lovely claw marks on one window - she's only ever done it once though. I think she scared herself falling in the sink)
Here I have it on the bathroom window despite the swirly glass as quite frankly you can see that you are naked in the bathroom with just the swirly glass. So bathroom and en-suite.
I also have it on the half glazed door that looks into the garage so that you can't see what is in there and on the two panels of glass in the front door.
In my son' school they have the mirrored privacy film, so from inside the classroom you can see out, but from the playground you are just looking at a mirrored surface. You can tell the windows are tinted this way. But when you put the light on, it is like having nets so if it is dark outside you can see in.
This video on YouTube shows you application and the difference.
As the film can be peeled off, you could always order the smallest quantity and apply it and see what you think. My bathroom and en-suite ones here have been in place for 4 years and still look fine.