Used the prep machine from birth. It's amazing.
We live in the UK. Tap water is clean.
The machine has a filter.
The first shot of hot water kills any potential bacteria in the powder before adding cold filtered water.
Proper use of the machine I.e. regular clean cycles, using correct filters etc and you should have no trouble.
My baby has never been poorly with more than a sniffle.
We sometimes make up bottles in advance, cool them under the tap and store in the fridge before putting in a cooler lunch bag with ice packs for when we go out. We use a flask of boiling water to take the chill away.
Going against guidelines doesn't mean any harm will come to your baby. Hot water, clean hands, sterile bottles and cold storage are key if going against advice.
The guidelines tell you the safest and idiot proof way to feed your baby. It's not the ONLY safe way.
There will be absolute dimwits out there who will deviate from the guidelines but wont make up feeds safely. Perhaps don't practice good hygiene, or don't use boiling water, use cold water to make up the feed or might leave advance made feeds out at room temperature, so they have to be absolutely clear and strict in the guidelines.