While I've used 2filters.com as a source of filters for years in the past, their pricing more recently has not been as attractive/competitive as others. I did buy some B+W filters thru Maxsaver at substantial savings. Lots of rumors/debate at the time as to whether they were knockoffs or authorized distributors. Evidence points to being real product BUT definitely not an authorized distributor, allegedly sourcing B+W's thru relatives and/or a sister retail/distributor company in Asia (Hong Kong?). For a number of months they have not actually carried B+W filters although their site still lists them, although without pricing (ie not available).
B+W filter pricing is very "dynamic", ie constantly changing. Know what sizes and models you want and track pricing from Adorama, B&H, and 2filter to determine best source. Note that some sizes/models might be less at one source but different sizes/models higher....its specific! I most recently bought B+W's via Greentoe, supplied by Unique (UV) and Adorama (CPL).