This app was mentioned in 2 comments, with an average of 1.00 upvote
I guess I haven't tested the lower range of the Smart. Certainly they can all make Yogurt via the Yogurt setting, so they need to be able to hold a temp around 43C (110F). The 20°C lower limit is the lowest temp you can program with the Smart Cooker App (Android, iOS).
Really, I'm not sure what you'd do with the extra range on the low end, so probably Ultra owners won't miss it.
I finally found the Bluetooth version. This is the app. It seems that this is exactly what I was looking for. I think I'll buy one the next time I have to move.