I use birkenstocks. I have been through 3 orthodics from different doctors. I have really flat feet, and no orthodic has ever helped me, not even my pocketbook. Of the birkenstocks to buy there are really only three models that have kept the original arch. The milano, Arizona and Zurich. The original arch is of great importance for flat foot sufferers.
But hey think of this. You could go to an orthopedic specialist and get orthodics at around $1000 that includes doctor fees only to find out they are not correct for your feet and you need to find another podiatrist. Or, you can spend $100/ year on a pair of birkenstocks to wear indoors and outdoors and save yourself boatlodes of money. I try and buy two pairs each year.
I even chastise the podiatrists as to why I can spend $100 on Birkis and get better results than their multi-thousand dollar orthodics. Orthodics should be less than $300, but you have to factor in all the costs of x-rays and doctor fees. That's usually $1000 or more if they can't get it right the first time.
BTW if you like merrell check out
http://www.danner.com
Those masai shoes are developed in Switzerland. Swizterland has one of the highest standards of living in the world. They also pay their employees (contractors are uncommon in corporations) a livable minimum wage of about $20. That should explain the high cost of these shoes.