I visited Umm al-Jimal by rental car from Amman on a trip in May 2019, that covered the northern WHS of Jordan. Access was easy, even though it is close to the Syrian boarder and neighboured by a Military Air Base and a huge refugee camp.
Even though not as spectacular as nearby Jerash, the place has its charm. There is so much left from the Byzantine/Umayyad city, that it rather looks like a town recently destroyed by an earthquake than an archaeological site from the 6th century. On the other side I had a hard time finding something from the Nabatean and Roman periods. The real beauty of the city lies in the building material. The region was formed by volcanic activity and everything was built with local black basalt stones.
 
The site can easily be combined with Quasir Amra, As-Salt and even a few TWHS. There is not a lot of traffic outside of Amman, so a lot can be achieved during a productive day.