Stayed at both of them a few years ago when kids were younger. Full of Germans, but having stayed in another place in Holland at the end of UK school holidays it was quiet - the schools across there seem to go back earlier, dunno if they are more in line with the Scottish school holidays.
Food was cheap at first, then got more expensive to eat at the restaurant, but that was down to the prices for the kids increasing as they got older.
Beach is a few minutes cycle from Port Zeland - huge and empty. Wish I'd taken the chance to try a blokart (land yacht). They did hire nice keelboats out at CP - we took one out for a couple of hours. At no point did anyone as us if we could actually sail! Lot more laid back than the UK.
Port Zeland was also the shortest distance I've ever driven for a holiday. Couple of miles to ferry terminal and 20+ on the other side . By the time the ferry was included it wasn't any cheaper than the UK. But it wasn't the UK