The needle versus cannula question gets argued as though one is simply safer. It is more specific than that, and the specifics are worth understanding because they change where you should use which.
A sharp needle cuts. It goes where you point it, gives good tactile feedback about the plane you are in, and allows precise placement of small volumes. It can also penetrate a vessel wall, which is the mechanism behind vascular occlusion.
A blunt-tipped cannula does not cut. Introduced through a single entry point, it pushes tissue aside as it travels, and is less likely to penetrate a vessel. Less likely is the important phrase. Cannulas can and do enter vessels, particularly narrow gauge ones and particularly when force is used to advance them. A cannula that needs pushing hard is in the wrong plane, and forcing it removes the property you chose it for.
So the reasonable position. In vascular territory where you are placing larger volumes across a broader area, such as the midface, temple and jawline, a cannula reduces risk and is generally preferred. For small precise deposits, and where you need certainty about depth, a needle is often the better instrument. Lips are done well both ways and practitioner preference is legitimate.
What matters more than the instrument is everything around it. Knowing the vascular anatomy of the specific area rather than the face in general. Choosing the correct plane and confirming you are in it. Injecting slowly, at low pressure, in small aliquots, with the needle or cannula moving. And stopping immediately if the patient reports pain out of proportion to the procedure, or you see blanching.
That last point deserves emphasis because it is the one that actually saves tissue. Occlusion managed within minutes usually resolves. Occlusion managed within hours often does not. A practitioner who is watching the skin and listening to the patient will catch it whichever instrument they were holding.
Gauge is worth a thought too. A larger gauge cannula is more likely to displace a vessel than enter it, which is why very fine cannulas give away some of the benefit. Match the gauge to the product and the plane rather than defaulting to the finest available for comfort.
Entry points are the practical downside of cannula work. You are making a hole with a needle first, and that hole bruises and sometimes marks. Plan them where they are least visible and tell the patient in advance, because an unexplained pinpoint mark reads as a complication.
Whichever you use, aspirate or do not, but know why you have chosen. Aspiration before injecting is contested, with reasonable arguments that it produces false negatives and reasonable arguments that a positive tells you something important. What is not defensible is doing it without knowing what a negative actually rules out, which is less than most people assume.