How safe are botox/dermal fillers training course?

See trained Plastic. If you are asking whether you should be a patient in a dermal filler or Botox training course then that would depend on whether you already know the plastic surgeon/derm md ;they are having you trial a new product after having discussed all the risks, benefits and limitations with you. If it is someone that you don't know or at a med spa, then stay away as non-specilaist are trying to learn on you.
Botox/fillers. A weekend course may be fine for some things (painting, cooking), but not for medical treatments. See a board-certified plastic surgeon or dermatologist for your Botox or fillers. Avoid medspas unless affiliated with a plastic surgery or derm practice.
Be careful! Make sure whoever treats you is a board certified facial plastic or plastic surgery, or dermaotlogist experienced in aesthetic treatments.
Safe for who? It all depends on the instructor. If you have a good instructor and a small class, then very safe. If you have an unskilled instructor and too many students then its virtually impossible to get adequate (much less good) training. Even so, these products are very safe. You may not get great results, but serious injury would be very unlikely.