With the UMP on the Ronin S you'll be holding and trying to control more than 10 pounds of top heavy weight using a single arm out in front of your body. Perhaps you are superhero strong, but that will be really tough for an average mortal to do for any useful length of time.
I've got a Movi M15 and even though the Movi itself is light and offers handles to hold it with both arms, the Ursa Mini Pro really is just too much weight to carry easily.
You might look into getting a used Letus Helix. I've used the Helix junior with the BMPCC and it worked really well. The compact size and ability to set it on the ground are advantages to the Helix over a Movi.
If you do end up putting an Ursa Mini Pro on Ronin-S, please do let us know how it goes.