Filtering is good if the traffic is stationary. You just pay attention to what's going on INSIDE vehicles: is someone trying to exit a stationary car, spit through the window, turn right/left (you see wheels turning usually, driver checking mirror - sometimes) etc. So do it slowly, carefully, expect people to do sudden things.

When traffic is moving, even slowly, filtering is not very wise. I do it, but rarely on those occasions.

Be aware of your surroundings, look and plan (far) ahead (I got stuck between two rows of cars just as the light turned green, with a bus to my right - not very smart).

I filter on a bicycle, motorcycle. Those who think it's not fair: I filter and get out of the way, try not to slow people down or punish them for letting me pass through. If that's not fair, than drivers should open their roofs to let the rain fall on them too and never drive faster than 30 km/h - so we're all equal.