The need for filtered or unfiltered seems to be cause for a lot of discussion around the groups that I am involved with. Some swear by the need for special (expensive), custom made filters and others are adamant that standard plugs are fine.
Personally, I use some simple silicon re-usables that block out a lot of volume, and it doesn't seem to interfere with my ability to hear traffic, sirens or anything else. The only time I occasionally wish for a different plug is if someone tries to talk to me with the helmet on, that can be tricky!
Over the years, I must have tried around twenty or thirty different plugs, and the very best are some blue disposable foam ones by a company I can't find!! There are a bugger to fit at the roadside though.