Mandalorian armor is actually fairly high-tech, especially the helmets. Notably, the helmet feeds in a lot of additional data to produce a continual heads-up-display that they rely on and offers additional viewpoints - the visor, which would appear restrictive, doesn't actually limit field-of-view at all. As a result, removing the helmet is rather like willfully putting on an eyepatch and the Mandalorians feel deeply uncomfortable without it (this is also, to a somewhat lesser extent, true of stormtroopers). That said, they do remove the helmets and armor in private and when completely secure. It's notable that this first episode fades to black during the period of time when the titular Mandalorian is alone onboard his ship with nothing but carbonite corpsicles. He probably took his armor off then.

Also, Traviss is hardly the only source, or even the principle source on Mandalorian culture. Dave Filoni, who directed this first episode and whose stamp is all over it, did his own work with Mandalorians in TCW that did not mirror Traviss' take (and I don't mean Satine's crew, but rather Bo Kataan and her bunch), and seems to be drawing from throughout the EU for inspiration.

This episode is very solidly in the Star Wars as space western camp, which feels right for a TV show. It also very much has the feel of a number of EU stories about bounty hunters, and not just Boba Fett. Both aesthetically, with a lot of practical effects and a bunch of familiar non-human species, and thematically it feels much more like a story set in the EU timeline shortly before and after ROTJ than anything previously produced by Disney. Personally, that's a very good thing.