We love our rapid cool. I use it both ways. The second way means you can reuse as much as you’d like (although the bottle needs three hours in between use to ensure the temperature cooler is working properly). If you hot shot and cool the rest using the nuby, make sure the hot shot has cooled a little as it might still be too hot for baby with the rapid water (I hope that makes sense). I also sometimes make her bottles with hot water and leave to cool in cold water, but that requires planning and sometimes I’m not that organised and time runs away with itself so the nuby is great for a quick work!
My baby is on 240ml bottles and we use the Nuby for every feed. I do 30ml hot shot with formula in the bottle and the remaining 210ml to cool in the Nuby. That way as it’s only had boiling water in, I can re-use multiple times in the day and then I sterilise overnight. Comes out the perfect drinking temp too!