I changed a 50/34 to a 40 and don't get any noise at all. Using largest cog on cassette looks like a bad angle but it makes no noise and I don't stay in it long.
I also kept my 12 - 25 11 speed cassette with single steps from 12 to 19 and love it. 40 is almost in the middle of 50/34 and I don't miss the double at all, 40/12 is enough for me on mostly gravel/single track and 40/25 gets me up every hill where I live. Shifting the front ring up was never comfortable as I have a broken middle finger so in my case no negatives.
I changed a 50/34 to a 40 and don't get any noise at all. Using largest cog on cassette looks like a bad angle but it makes no noise and I don't stay in it long.
I also kept my 12 - 25 11 speed cassette with single steps from 12 to 19 and love it. 40 is almost in the middle of 50/34 and I don't miss the double at all, 40/12 is enough for me on mostly gravel/single track and 40/25 gets me up every hill where I live. Shifting the front ring up was never comfortable as I have a broken middle finger so in my case no negatives.