NCT classes?

Hi all, I'm umming and ahhing about whether or not to register for NCT antenatal classes (probably a question for UK people, I'm sure others have no idea what I'm talking about!) - it is my first pregnancy and I dont really know any other mums/pregnant people in the area but the course is just so expensive, I cant decide if it's worth it. Would anyone be able to share their thoughts and experiences. I need to decide in the next few days as they are keeping the last space for me till Saturday, it seems these things get sold out really quickly. I know that there will be classes also available on the NHS, is there a massive difference? If anyone has experienced both options it would be especially helpful.