They are getting stricter and there is talk that the visa runs in HK will be abolished in the future. If you can, start the process from your home country. Some get through some not. If you are willing to risk it ... use a visa company to do it for you.

To avoid taking two medicals, go to mainland China on an L. Teach there and take your medical there. Then go to HK for your Z, or to another third-party country bordering China. But the times they are a changin - I fully expect things to have been tightened up by the time the amended visa regulations come into effect in the spring of next year. It is probable that the Chinese government wishes to exercise stricter controls at the borders of China. They must be aware that many foreigners in China at present aren't the kind of experts they are wishing to attract. They'll lock the stable door after the horse has bolted.
Many thanks for your input.