Just one data point, but it's a bad one. I'll be passing through Paris for only one night in June. A ballet performance on that day is sold out. I called Concierge; agent said she'll talk to brokers they use. Next day she tells me the brokers tell her ballet is sold out (uh, thanks). She can't find tickets.

So I spend about 20 minutes searching on my own, and I find a broker with tixs. Not cheap, but it's done. I don't understand why Concierge couldn't figure this out.

Still, I'm generally very happy with my AmEx Plat.