What adapter do you recommend?

You'll only need this:
https://store.ricksteves.com/shop/p/european-power-adapter

Do you really need 6 USB ports and no plugs?

You just need to make sure that the adaptor has a plug that fits the country or countries you are going to. Most European countries use the round two-prong, but it's easy to find out. If you are going to multiple countries that require more than one adapter, you can buy one of the multi-use ones that are all over the place. If you're just going to the Netherlands, it uses the round 2 prong plug, so make sure your adapter will work with that. The one from Rick Steves in the previous post would certainly work and that's a great price. I used a similar one for all my electronics (including a 4-port USB charger), so I'm sure you won't have any problem.

The link you posted ( https://www.amazon.com/gp/product/B01MTS2WUA/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 ) has lots of photos, and says "110V to 240V input", but misses the second bit of information you need to know: what sort of plug does it have? Is it 2-pin or 3-pin? Is it a North American plug, or some other type?

If it is 2-pin North American plug, then a 2-pin adapter like the one posted above ( https://store.ricksteves.com/shop/p/european-power-adapter ) is OK.
If it is a 3-pin plug, you need a 3-pin adapter. The Netherlands uses "Schuko" (aka German) plugs and sockets, so you would need an adapter for Schuko.