Both sources for downloading V4 maps are good BUT...

Downloading directly from Openandromaps requires downloading a package of some countries that are not always desirable and not required either because of its weight.
Spoiler: Openandromaps 316 mb
openandromaps V4

Direct download from Index allows you to download a map of each country, individually.
Spoiler: Index 59 mb
INDEX V4

The advantage between them is clear and given to the user's choice.