You don't need a regulator to fill tanks since the pressure doesn't matter. The pressure *does matter* when you're connecting your interior plumbing to the outside source.
The one you listed will work, but something that tells you the pressure you are putting into your RV would be better. amazon.com/gp/product/B01N7JZTYX
No moving parts so it will be about as “reliable” as you can ever get. Is there a reason you only asked about about “refilling,” meaning the fresh tank? You should have a regulator for ALL the water uses in an RV. PEX plumbing in RVs is really only rated to handle about 50 psi; I’ve seen parks where the hookup gave over 100 psi. BTW the regulator should be on the park’s valve, not downstream at the RV.
FWIW here is a good regulator that I use. https://smile.amazon.com/gp/product/B01N7JZTYX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Get one with a gauge that you can adult. The one you are showing is a static pressure whatever the maker sets it to and prone to breaking in my experience.
Walmart sells that in the RV section.
Here is what I am talking about.