Here goes what I can say based on my experience.
One of my listings is a studio that has a small bathroom. The layout is the same as the picture you put in the opening posting. Anyway there are basically 3 differences:
1- In the small batheroom of my property there are more room between the washbasin and the toilet and it is a bit less narrow. Honestly speaking, considering that type of layout (shower box, washbasin and toilet in line) I think that less than 1 meter wide X 2,4 meter long is not recommendable. ( Anyway, if it is not possible, 2,2 meter long can be acceptable). Having this measures, the bathroom can be very functional, except for people that may have mobility difficulty and overweight people.
2- I have installed an sliding door. Sliding door is much better for small bathroom or even small kitchen. Other type of door are not practical in terms of normal usability for small rooms.
3- The mirror in my property is above the washbasin. Actually, it must be above the wash basing otherwise it is not functional.
Most of my guests are from Europe, UK, Brazil and South America. As for guests reaction, I have never received any complain about bathroom dimensions! If you show the pictures properly in the listing, the guests will see in advance the type of accommodation they are booking. So, when thay are staying, if they find something functional and pratical, there will not be complains.