Landfall

In addition to giving the ability to purchase all of the 3-piece class ensembles, it also gives the ensemble for the current class. This combined with it not being an account-wide achievement means you can repeat this on each class and save the 4k bronze per set.

If you haven't done this faction on live and gotten the double rep token before, you will hit exalted when turning in the 2nd to last quest of the campaign. And since you need to do 2 things for this achievement and 2 of those are the campaign and get exalted, simply completing the campaign will finish this achievement. Took a hunter through as a 2nd character with the starting base 100% exp cloak and it took about an hour to get to level 20 to start the Landfall campaign and another hour to do the campaign.

Note that the Isle of Thunder achievement is the same but for the class arsenals, but Isle of Thunder is scaled for level 50+ so will take a good bit more effort to level alts through just for the arsenals.

EDIT: As an addition to the class arsenal, I ended up with slightly over 5k bronze on the alt getting to 20 and through the Landfall campaign. The class arsenals then sell for 3k bronze (the ability to buy them is an account-wide unlock). Could run through getting the ensemble for free and just buy the arsenal and still have a couple thousand bronze to spend on other stuff.

I just barely dinged 30 at the end of the ensemble run.

The reputation is bugged. Both the dailes and questline "Campaign: Landfall" have been reduced to 150/250 reputation. After completing the 12th step of the questline I should have recieved 3000 reputation for Operation Shieldwall. I did recieve 3000 but also got 2750 reputation decreased. I've never before had reputation removed after finish a quest, this has to be a bug from patch 11.0 as other post also recognize. I've made a ticket of this to blizzard and i've posted a Screenshot about it on this achievement.

Completing this achievement awards the ensemble for whatever class you finished it on.
For example, I got: Ensemble: Aldrachi Blasphemer's Flames

I was previously under the impression that you had to complete the achiev just to be able to buy it so wanted to share!