It's still maintained by the Free File Alliance. So you're giving your data to a third party that's not the government. I use it, but I would rather I didn't have to share my financial information with third parties to do so.
No matter what, you will always be using software and systems controlled by other entities. From you web browser, to the operating system, the data transport links, routers and switches in between, and when the data gets to the destination the software is typically written and maintained by commercial contractors hired by the government.
Right, but I would argue that this is more explicitly "putting my data on someone else's server." If it was a government server, well, it's there already anyway.