I've never been to a Servisair or Menzies lounge on the Schengen side. On the non-Schengen side the two have merged and moved into the old KLM lounge which is quite a nice spacious room (I used it when it was a KLM lounge)

I used the Servisair lounge a few times in its old location (using PriorityPass) and there was no need to prebook. Facilities were nothing special, but there was the usual range of drinks, and there was some food (bread, cheese, ham and various cookies and nibbles IIRC)

There is a "rest area" with reclining chairs on the top floor of the non-Schengen side (or there was last time I looked), no free refreshments but a reasonable place to hang out for a few hours if you can't get into a lounge (or if you get kicked out after three hours). There are also public showers on the top floor of the non-Schengen side.