MS has S&B filter...according to tests done by S&B, particle filtration is slightly better than K&N (filter used by Dinan) or AFE. S&B uses exact same material on all their filters and they post comparative tests for their direct sold filters for trucks on their website. The MS and Dinan intakes have a similar larger cross-sectioned elbow design.
There are several videos out there with Steve Dinan and how Dinan improved upon the E60 M5 intake. These videos demonstrate 1) not all hp is necessarily maxed out by the factory for many different reasons; 2) improvements are possible and testable; 3) Dinan actually spends so much time engineering stuff like intakes and every theoretical design is tested in the real world and oftentimes they have found designs that theoretically should have worked better but didn't in practice.
The facilities that Dinan has in Morgan Hill and what they do for racing and street (both BMW and other engines such as Ferrari) is impressive and probably the best outside of Europe, so when they say something (or produce something with advertised hp gains, which btw happens to be smaller vs everyone else's), chances are it's pretty credible.