yes, li is way more thorny than lang, but lang may also have thorns while young.
can you post a picture of the thorns of your tree? jujubes generally have asymmetrical thorn pairs on their laterals, and li tends to have one straight dagger and a curved one per pair, while lang tends to have a slightly crooked one and a curved one. .
li is a proven self-fertile cultivar, and may well be the best juju for beginners or if you only want one tree.
lang seems sterile on its own, but like @k8tpayaso said, it is best to have more than one cultivar, since it helps gets rid of the paranoia. If you only want one tree, and are handy with grafting you’d find that jujus have high success rates.