soft shells are restricted in many places, be very careful when importing any turtle species with regards to endangered status and local legality.
That said, soft shell turtles are mean as hell and most aquatic turtles do a fantastic job up fouling up water quality in rather short order. So you need to be prepared to potentially be bitten, which can cost fingers, and to deal with the fallout of turtle water. Other than that, they will take down any prey they can. That includes arrowana, so be warned ahead of time they can do a lot of damage to fish even larger than them in a very short time.