I've lived in Hillsborough for the past 25 years so I'll chime in as a frequent Manville visitor.
It's a decent small town with what appears to be a great place for a 1st time home buyer since the homes are "starter home" size. Some of the old Polish population is being replaced by Hispanic. I believe Frank's Chicken House has been gone for a few years. The Chester House was knocked down and the site is now a Royal Farms / gas station which is a huge upgrade. I rarely hear about any notable crime issues. I have a co-worker who lives off Camplain Road and loves the area. They've been upgrading the main street with pavers and this has caused some of the traffic issues there but traffic is a pain in the *** there at rush hour. I don't know about school ratings but a friend's son is a teacher in Manville and loves being there (note that his 1st teaching job was New Brunswick). As others have stated, beware of the areas that are flood prone. Specifically, the Lost Valley section, parts of Main Street and Dukes Parkway East which includes that section of Hillsborough. If I stay in the area when I decide to downsize my house, Manville is a possibility for me.
Good luck to your son.