Personally, I have done a fair bit of temple filler injections and volume restoration of the temple with fillers. It does give a good result generally. It is also generally safe with minimal side effects. Some of these minimal side effects include redness and bruising. Some patients do feedback that they do get a bit of pain and discomfort. But it usually resolves after 24 hours.
Some dangerous complications may include blindness. However, it is extremely rare and usually, experienced doctors know how to minimize these risks as best as we can.