For while now I have been using ezpublish as a framework, and CMS when my web projects are based on PHP, and I must say, I have grown accustomed to it because of its flexibility for most scenarios.
However, I've had to build e-commerce sites now and then, and ezpublish includes a webshop that caters for the e-commerce needs of your installation, and of-course with all the tools you need to extend, should you need to.
Is it worthwhile and optimal to use the inbuilt webshop for an e-commerce solution, or should I rather go with an all out e-commerce solution like Magento, which has made a significant impact in that sector?
Magento is great. It's chock full of features that you would normally pay a lot of money for in a shopping cart (or spend an eternity implementing yourself). Mostly anything you don't have in the base installation you can get from the community.
But it's extremely complicated. Expect to step a lot of time setting up your store, as the default install is not ready to go. Expect to spend time adding a template, which will take much longer than you expect. Expect to stretch your PHP skills in ways that you cannot anticipate.
Generally, Magento is not the "fast" option, nor the "easy" one, just the good one. If none of that dissuades you, it's a great option :)
Hope that helps. Thanks, Joe