I live in CA where we have to use bear canisters, so take my input with a grain of salt. The one time I used a bear bag and researched it Lawson's string was very popular:http://lawsonequipment.com/Ultraglide-Bear-Line-c148/
I ended up being in locations with a bear pole and didn't actually use the string.
In terms of barrier bags there is no definitive answer as far as I know. I think it mostly comes down to the bears you are dealing with. What is clear to me is that barrier bags reduce smell but do not eliminate it. Bears make an assessment of how much food there is before deciding whether to go after it. A barrier bag in that way may discourage many bears even though they can still smell the food. So, IMHO, barrier bags may work well, but can still fail particularly in places where bears have reduced fear people (and are willing to take more risks to get people food).