As for trunk stability this bike is easier to use than a trike because you lean into a turn. The force generated by a turn never tries to push you off the bike, the bike is always under you since it leans with you. A company called Varna makes some 2 wheeledhandcycles right now, but I am told they are not able to be ridden by anyone without use of their legs.
Our experience with the test bike was that it was impossible to get seated by yourself without the landing gear but once you were in it riding was not a issue. It felt stable at slow speeds in spite of the flexible attachment.