I've been to 4 group classes exclusively for the erg. Mainly to make sure my form and shyt is good. Once i get 4 more in (end of this week) I'll just go from there and do the rest at home.
Protip: search for free classes in your area. Most places will do a full class/session for free. I did two at other places before i found this place. They are all pretty much the same.