"Fast transactions"
Fast transactions implies it is slower than Visa, and Visa is 'instant' by comparison from the spender's POV. Bitcoin is still very instant because wallets still send notifications/pings when transactions are first seen, not when it goes into a block. We shouldn't mislead people into thinking a transaction literally takes 10 minutes to travel the globe.
Maybe this feels like PR speak. But being too humble about Bitcoin's attributes isn't a good idea either.
If we're going to look at perception, image and expectations, perhaps we can start to look at redefining some terminology too. Like confirmations, which is an arbitrary concept. Where possible we should describe it with finance terminology.
"0 conf transaction"
0 conf is the 'transaction' - just the act of making an exchange. It doesn't imply safe and I believe using the word 'settle' in place of confirmations will automatically click with merchants.
"1st conf"
A 'confirmation' is a 'settlement'. If it is 'settled', it implies final (except by court order), whereas confirmation usually means 'ah, I've seen it come through'. I rarely hear any sales clerk call credit card transactions confirmed. More often you will hear 'approved' instead. Although 1st conf can be overtaken, so...
"n confirmations"
This term can probably stay since I can't come up with a better word. Settlements only happen once, putting a number next to it breaks the meaning of the word. "Settled with 4 confirmations" seems pretty clear. Alternatively I think instead of displaying a meaningless number we ought to go by a percentage (the double spend improbability) and go by 'confidence'. "Settled with 92% confidence." Or we can pick an arbitrary number like 6 and use 'settling...' and 'settled' when reached.