I haven't tried any of the mixes. This is the one I always make & it's easy:

LEMON BARS DELUXE
2 1/4 cup flour
1/2 cup confectioners' sugar, plus additional for sprinkling
2 sticks butter
4 beaten eggs
2 cups granulated sugar
1/3 cup fresh lemon juice
1/2 tsp baking powder
Preheat oven to 350°. Whisk together 2 cups of the flour & the confectioners' sugar. Cut in the butter until the mixture clings together. Press the dough into a 13x9x2" baking dish. Bake 20-25 minutes or until lightly browned.
Meanwhile, beat together the eggs, granulated sugar & lemon juice. Mix the remaining 1/4 cup flour with the baking powder; stir into the egg mixture & pour over the hot baked crust. Bake for 25 minutes longer. Remove from the oven & sprinkle w/confectioners' sugar. Cool. Cut into squares.~~From Mountain Measures.

Luscious Lemon Bars

1 (18.25 ounce) box yellow cake mix
2 eggs
1/3 cup vegetable oil
8 ounces cream cheese, softened
1/3 cup granulated sugar
1 teaspoon lemon juice

Mix dry cake mix, 1 egg and oil until crumbly; reserve one cup of mixture. Pat remaining mixture lightly into an ungreased 13 x 9-inch baking pan. Bake 15 minutes at 350 degrees.

Beat cheese, sugar, lemon juice and remaining egg until light and smooth. Spread over baked layer. Sprinkle with reserved crumb mixture. Bake 15 minutes longer. When cool, cut into bars.

These are really good!

Marilyn's Lemon Brownies