Interesting. I checked it out a little...
It`s hard to tell exactly what features are included... specifically, the important feature of an ecommerce site are to have complete product and customer databases access and control (edit/management).
In addition, there should be the ability to use a SSL... not sure if the script is compatable either.
PS: I`m going to download it an do some "testing".
The plug-in ecommerce is ok. It is easy to install, set-up and add products and pricing. The drawback of it is it does not maintain a customer database. So, if you want to keep a record of people who purchsed products - to email them at another time about sales, or news (other marketing), you need maioltain that information separately.
The advantages of using an ecommerce application like osCommerce, Zen-Cart, Xcart, etc is they maintain a product AND customer database as well as keep track of all sales, even hit on your products.
The wordpress plugin does provide a CSV file (of customer information) to download.
It all depends what features you want for ecommerce. If you do not need a customer database managed by your ecommerce solution (or are willing to maintain it separately), the the plug-in is ok.
This is "just" a "plug-in" (added script/files) that enables you to add ecommerce-like features to your wordpress website.
Like there are added modules or script you can add to osCOmmerce, Zen Cart, etc to preform tasks the default program does not contain.