Yes, Parish Online is a great way to cost-effectively produce maps for use in Neighbourhood Plans.
How far you take it is up to you. You can simply use the Print and Export features to produce a map of your Local Council displaying your boundary, or you can create additional information such as neighbourhood boundaries, proposed development areas, locations of amenities etc to layer on top of the map.
Every Parish Online account contains high resolution mapping from Ordnance Survey and Getmapping, as well as layers of constraints information such as Environment Agency flood areas, crime statistics from Police.uk, SSSIs and Ancient Woodland from Natural England, as well as many others covering England and Wales.
If you're worried that this might be too complex, be assured that we have tutorial videos and FAQs to help you become a mapping professional!
Here's a screenshot of Parish Online showing the extent of Environment Agency flood risk combined with some (made up) sites for proposed development.