Group RESPs are a bit like a true mutual insurance company.
You all pay into the fund, and then, depending on the number of kids that are in school that particular year, you get paid a certain amount.
Advantages could be that if you end up with one or two years of only your kid in school and nobody else's in that age bracket, you get more money.
Disadvantage for the same-reverse reason also could be true.
Another advantage of regular programs, unlike pooled, is that if you do not use all the money, then some/all of the remaining funds may be transferable to an RRSP.
Personally I would not invest in one, unless it was more like a specific investment-club that I knew everybody.