Has anyone tried the new flea collar Seresto and what are the results?

I have large dogs, Labs, and live on a farm on the lake. They are outside a lot and in the water a lot. The only thing I've found in recent years that works for fleas is the Comfortis pill. Drops and collars have not worked here in years. Advantage worked when it first came out, but something changed and I don't think my fleas got smarter. Feed back on the particular product will be appreciated. I don't need any advice on natural remedies. I've tried everything and even flea dip does not work here any more.