It is simple, it works and if you expect more sales…

You can easily migrate to Cart66Pro which isn’t loaded up with a “buy by the part” mentality. If the developer had a community supported forum, it would get 5 stars from me. I have no vested interest in the product other than my sanity when developing for clients. If a client is on a tight budget and uses PayPal Standard, this is easy, fast and free.
Be sure to download the PDF, it addresses darn near everything you could run into.
The nice upside is that you can configure variations and shipping pretty easy. This is especially the case when you have items with multiple variations and prices, such as three sizes and colors of one item. I’d rather not write some crazy short code per item. Instead with Cart66Lite I enter the products into the back end, create my page of products and then use the icon near the post/page “insert image” to insert the item I want.
In particular shipping options are pretty robust if you don’t want to mess with live shipping. Default by the piece with bundle for additional items is again, very easy.
I am not an affiliate, don’t have any financial interest, or know the developer. I do have a sense of sanity when it comes to my time.