I’m based in the US. My totals are exactly the same regardless of whether “Treat transfer fees as disposals” is turned on or off. Also, even when it’s on, each transaction fee is shown as a disposal anyway.
I’ve read in the forum that the feature is disabled in numerous countries — but it sounds like they weren’t able to toggle it on, or that it auto-toggled itself back off.
If this feature is also not available in the US, I would suggest that it be totally greyed out or not even shown if the user choose an incompatible country.