I took Imogen at around a couple of months old for 3 months and we loved them. I thought they were well worth the money. When OH was at home with Lo when I went back to work FT he went along with her and thought they were a waste of money! His reasons were that the woman running them didn't do much, all she did was give things out and let the babies play (er....yeah that's the idea!) and there was a 20 minute break in between (where babies and mums could play on mat/in ball pool/with mobiles/puppets etc) while the woman set up the next activity.
I think he missed the point that the 20 min break was for the mums just as much as the babies to network and speak to another adult! Also, I probably have a better overview of how important those very simple but early interaction/sensory activities are for young babies and it was those sort of things the lady was doing (e.g. blowing bubbles, exploring sensory toys, balloons, light shows etc.) So I think he missed the point a bit. he preferred the music session we also used to attend where two women spent the whole 50 minutes up singing and prancing about to songs/music and we listened, joinign in where we wanted. I think he felt they "earned" their money from the fees more. But to me, it was about what Imogen got out of the sessions, not getting our money's worth as the 1st priority.
I say "go for it!" - you can do a trial sesion first at most classes so maybe do that and see what you think?? x