A department store bike will work fine and be safe as long as you go over it and adjust anything, but the poor finish might bug you. My son’s first bike (Toys r Us) was so misaligned that the front wheel was over a half inch to the left and the rear wheel almost a half inch to the right (frame alignment, not wheel true). He had no trouble riding it, but it bugged me so bad that I got him a quality used bike (Merida) next.

Keep in mind that name brand bikes have resale value, so you’re getting a chunk of your investment back when you’re done with it (most or all of you also bought it used). Used BSO’s won’t fetch much at all.