First of all, there is no law governing the length of an engagement. One can get engaged, and be engaged for as long as one wants or needs.
Secondly, there are no laws prohibiting the termination of an engagement should the match prove unsuitable. Just because you get engaged, doesn't mean you have to marry him if somewhere down the line you find there's a compelling reason not to.
My point being, if an engagement will please your parents, I see no harm in it. You needn't do anything you don't wish to do, and you get a pretty, pretty ring into the bargain.