Well, only the difference in taxes actually.
I was recently in need of a flight from Kilimanjaro where I was on safari as well as climbing the mountain, to Brussels, Belgium where I was planning to attend Tomorrowland. Posts on those trips to follow. The cost to flight that route in business class on Star Alliance is 52,000 Singapore miles, which is the lowest easily obtainable currency. I searched for availability and could only find reasonable flights for my date, with the last inter-Europe segment in economy. The routing was JRO-ADD-MXP-BRU, so I figured a short 1 hour leg in economy wouldn’t be too bad.
Booking mixed cabin awards on Singapore is a little tricky, as you can’t book online, and have to call in. Furthermore, some agents seem poorly trained and will price each class separately. I didn’t have any issues though, and booked for the right mileage and slightly more fees than I would have paid with United.
Later on, as the trip got closer, I noticed that the MXP-BRU leg opened up in business class. I was wondering what it would take to change up to that, as by their award fee chart, it indicated that changes on partner awards might be US $50.
However, when I called in, at first the agent wasn’t sure what the change fee would be, if any, but after connecting to her ticketing desk, it turned out to be only 17 SGD or 12 USD or so. The change was processed almost immediately. So good trick to know if you end up initially booking mixed class through Singapore Airlines!