Turns out it's not quite two bathrooms... But let's start from the positives. The place is in a great location to enjoy Rome: quiet, surrounded by local amenities and well connected to the centre. The flat is modernly furnished and, though it doesn't get much sunlight being on the lower-ground, it's very well illuminated.
Now the issues. The toilet in the second bathroom relies on a mechanical pump machine to be operational. That machine is very delicate and requires a lot of maintenance. It broke after very light usage on the second day of our stay, almost flooding the toilet. The host sent a technician the day after, who was able to temporarily unblock it, but told us it was likely to break again, as it is old and in need for replacement.
That was particularly unfortunate to hear, given older reviews pointed out the same issue. And as the technician predicted, the toilet broke again after very few uses.
When I asked the host to provide us with a discount, I was astonished by their response. First, they offered the equivalent of two pizzas and beer, which was disrespectful of the number of nights we booked (13). Then, they tried to persuade us that we could do 'just fine' with one toilet, though that was obviously not what we paid for. Finally, they challenged us to find any similar place for cheaper in the area... Which, ironically, we did.
At that point, other minor issues that we were willing to overlook became more and more apparent. For example, the window in the only functional toilet was very tricky to open, to the point my girlfriend couldn't do it on her own.
Perhaps we have just been spoilt by great Airbnb hosts who always did everything they could to make us feel welcomed and comfortable, but the general impression, in this case, is that they were just... Not much bothered.
We ended up cancelling the remaining nights and moving to the new place we found nearby, which was absolutely lovely in every aspect.
Sadly, we had to pay for cancellation fees, even though the cancellation was not due to our fault. We contacted the Airbnb support, but they told us that they can only assist with issues that occur in the first 24hrs of the stay... Something to keep in mind for the future.
To conclude, if you are ready to potentially use just one toilet, and hoping that you won't have any other issues, you can hopefully make it work. Personally, I wouldn't book again.