Routing Supply Lines for Heat Pump Water Heater- Flex vs Hard vs ?

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I am replacing a water heater with top side supply connections with a Rheem heat pump water heater that has side mount connections. The Rheem design puts the cold water supply inlet right at floor level. The model I have has an auto shutoff valve which goes on the cold nipple and results in the cold inlet jutting out more than 6 inches from the tank.

Rheem recommends flex supply lines for vibration isolation. Apparently they have had some trouble with these units exceeding their rated noise levels, although from what I read, the noise problem does not seem to be related to vibrations transmitted thru piping.

I am a little bit warry about putting a flex line down at floor level, particularly because it would jut out into the room and be likely to get bumped or stepped on by foot traffic. Any leaks would likely not be over the drain pan because the inlet juts out so far beyond the tank. I live in an area (Massachusetts) where pros seem to do mostly hard piped and that is what I have done in past installs.

The options I have identified are:

1. Hard piped with brass 90 right at the cold water inlet to make the turn upwards as close to the tank as possible. This is probably what I would have done if Rheem did not suggest that flex lines are best. Risk of noise due to pipes transmitting compressor vibration I guess.
2. Stainless steel or copper corrugated flex from cold nipple to make the turn upwards. The flex is going to jut out into the room right at floor level. This is what Rheem is suggesting. Risk of flex getting stepped on or bumped.
3. Hard piped brass 90 right at the cold water inlet followed by short copper pipe vertical run followed by a vertical run of stainless steel or copper corrugated flex well above floor level for vibration isolation. Complicated. Weird.
4. Something with PEX. I know nothing about PEX and the house is all copper right now. Inclined to keep it that way.

What would you do here ? Is there a better way ? Anyone have experience with Rheem heat pump hot water heaters that can weigh in on the vibration risk with hard piping ?
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