First my credentials: I have written two fully complete and complex shopping carts from scratch and am currently working on a third. All three are very complete database driven carts that can handle a wide variety of product, shipping and customers and could be adapted to a site handling many thousands of products. The first one I wrote 10 years ago is still in use on my main site. It will be replaced by the one I am currently writing that will add significantly enhanced functionality.
Many sites have far less requirements and don't need a cart that has all the complexities like the ones I have written.
I downloaded and took a quick look at simpleCart. For those have the simplest of requirements, there is no reason why something like this can't be used.
For those of you that need a cart but don't really know what you need, I will give you some observations on simpleCart. These might help you in deciding your own requirements. Many of the things I say below may seem negative. I add them simply to let you know what other things you might want to consider when getting a cart. These are just a start to get you thinking. There are many, many more considerations.
simpleCart considerations.
1. Programming knowledge of javascript and HTML will be required to implement.
2. Checkout is through PayPal or Google. It isn't clear from a quick look if both can be used. You can't harvest your customer information (address, phone, credit card, etc) yourself.
3. No data is saved. There is no database connected to this cart. You will have no history on your site on what is ordered, who ordered it, where it is sent, etc. You will only know what is returned to you in your payment details from PayPal or Google. If a customer wants to reorder, save a cart for later, ask you about a previous order they are SOL. This is extremely important to many. If you want all your order and customer history to be in a database rather than emails from PayPal, you will have to manually input them into some database you devise. I get a lot of reorders where the CX says, I want to order the same as before - make it so. Can't do that here.
4. Taxes. You can set a tax rate but it doesn't appear that you can apply it to an individual state. You tax all or none. Taxes are applied only against product. You can't apply taxed against shipping.
5. All product pages will require hard coded HTML. Serving the product pages from a database would be outside the scope of the cart. Given this scope, this is best left to sites with very few (probably less than 25) different products.
6. Product is identified by name only. MPNs and other product identification isn't included. If you offer 12 different Van Gogh prints, then each will have to have a unique name. Otherwise when you get your order email from PayPal you won't know which one they ordered. Of course the customer will see item names like "16x20 Van Gogh print, moulding=xxx, outer mat=yyy, innermat=zzz, etc".
7. Shipping can be the most complicated part of a cart. That is why so many site use flat rate shipping. You can charge shipping as 1.) A flat rate for the entire order. 2.) A flat rate for each item (and the same flat rate is used for every item) or 3.) a % of the total order - not by individual items. You can't identify something as a 'Ship Separate' item like identifying that you can't ship a bowling ball and a bag of potato chips in the same box. There are no zone charges so everything is charged the same, whether it is next door or to Timbuktu. There is no way to refuse an order to North Korea or to charge more for overseas shipping. You will need to think very hard about your shipping costs if you use this or any of the other simple carts.
8. No inventory anything. Can't track what was sold, what's in stock or anything else associated with inventory.
9. No discounts available for quantity ordering. Nor can you bargain a price with a customer since the prices are fixed and you have no way to override them befor they are sent to PayPal.
10. No custom products. You can piecemeal something here by forcing the customer to individually order the parts that make something up. But lets say you are offering a framed item and want to offer them glazing upgrades. They would separately have to add the framed item to the cart and then go back and add the glazing upgrade to the cart. Since items are identified only by name, then you might have tons of items with the same name: "UV upgrade: would have to be "UV Upgrade for the Bierstadt 16x20 print with xxx moudling", etc,
11. No means to show an image of what they are ordering in the cart.
This is just the tip of the iceberg. I could drone on and one but its bedtime. The main point that I want to get across here is that choosing and implementing a shopping cart is a difficult task. If your needs are simple, then maybe something like this cart might suit your needs. If you plan on growing your site, however, then you need to put some time and thought into your cart. A shopping cart can be far more complicated than the rest of your site combined.
To be honest, if my needs were small enough to be satisfied by a cart like this, I would also consider alternative selling venues like ebay stores, rubylane, yahoo, aceseller and others.