If you are looking at possibly getting a LakeMaster mapping card then you are talking a Humminbird brand unit as they are the only ones that the LakeMaster cards work in. Humminbird units can use either a LakeMaster or Navionics mapping card. I recommend reviewing the lake lists for each mapping card to make sure the waters you fish on are covered to the level you want them to be (not just a lake outline). Then get someone to post or send you some screen snapshots from each.
Just a heads-up but the AutoChart feature from LakeMaster would make it possible for you to make your own lake maps.