I have never had any problems with the new express tools available. There are reasons for standard or web edition but a lot of sites could manage with the express edition.

SQL Server Express can be run as a windows service, just like the standard edition. It will llisten on the same tcp port as the standard edition. All tools that can connect to a standard edition can be connected to a express instance. There is no difference on how the service operates or how tools connect between the standard and express editions. Even the database images (files) can be moved between the standard and express editions.

Sounds like you have been using it as a file based database or the compact edition. The express edition is practically the same as the standard edition, but with some limitations on database size and what kind of load it can handle, If your customers site is within the limits, a standard edition is a waste of your customers money.