use it with care, not force
You would need to be extremely careful with a metal tool. The jets are made completely out of plastic, and a metal tool would easily deform it.
A deformed jet "hole" would either mean the water sprays unevenly, or just plain wrong and miss the windshield completely. It could also easily cause a clog or partial blockage depending on how the plastic deforms.
The safer bet would be using something as thin as possible like a needle, or somethin made of plastic like bristles from a kitchen brush or a toothbrush. If this doesn't help, replacing the jets is the way to go.
This is tho if your jets even clog in the first place. Here in German people usually use distilled water to mix with the additive, as tap water is extremely hard and would cause limescale buildup.
just use a good screen wash additive to keep the water clean
Only with distilled water.
Not everywhere drinkingwater is free of lime.. (hard water)
Like I said above, here we usually use distilled water. I don't think anyone should risk tap water, unless they know with 100% certainty that their tap water is soft.
I used to carry spare jets in the car when I had a CItroen
This is the way to go I think, if you have issues with the jets. I imagine it's not that complicated replacing the one on the Panda. Plus the fact that you can adjust it with a flathead screwdriver means you would have an easy time aiming it after replacing.
ensure no rubbish gets into the water
I don't know about y'alls Pandas, but mine has a removable screen inside the filler tube. Bigger debris would be caught by it and not end up in the tank. It might not be fine enough for sand or something similar tho.