First, I would like to thank you for this kind of script/application. It was on my queue for awhile as a project to be implemented.
Regarding the design quality. The design is simple and clear and easy to follow. This is what the end-user wants.
For the documentation, it is well documented and easy to follow. I just hope that you add some general documentation (not how to) but where to work on for the developer. For example, most people want to add payment method, or do some customization. So, build such abstract/general documentation as "where to" based on your clients feedback.
Most of the feature are available and good to start your business with. I believe you might need to add more features based on your clients' feedback, and I believe you will do it in the future versions.
Even though you do not provide customizations within your support, and I agree with you since this is out of the scope of the regular support, and it is considered and code maintenance after release, which you have the right to charge for. But, the code open source and customizable as per your license conditions, which is an advantage for your product.
Regarding the code quality, I consider it as a high quality, neat, clean coding, arranged, easy to edit (even in some cases I have to use the "grep" command to find the location of some part of codes, but this is not an issue since no developer documentation provided, which I hope for it in the future).
Bugs, until now, I haven't seen a critical/major bug. Even one found, you fixed it ASAP.
With Laravel, the project is so flexible and scaleable. Also, the developer is so flexible in maintaining the license multiple times in case of multiple re-installations.
I got your customer support multiple times with responses, either fixing in the nearest release, or guiding us on the application usage. Fast response within 24 hours.
I hope you won't stop adding more features improving your project.
Wish you all the best.