It is true that a properly aligned MB will stay aligned for years. My 12 year old 300E has never been touched. My wife's '84 190D arrived with the front end out of alignment. The dealer said his alignment guy was on vacation and I should take it to a shop he recommended. I did that but that didn't fix the problem. When the dealer's alignment guy came back, they aligned it and it stayed that way until I sold the car 17 years later.
Take it to a dealer and have it done right the first time. You should only have to do it once. It's a case of pay me now or pay me later with MB alignments.