I have. All of the plain text accounting packages are optimizing to solve the exact wrong problem. The reality is that even if you are using a commercial package, it's generally not hard to get a CSV (or something like it) OUT of the software. What you actually need for a sufficiently complex financial life is
input validation, and that's exactly the problem that plain text accounting software punts on.
Gnucash has a lot of cruft and definitely feels like it was written in 2003, but it does address this issue and provides the basic input validation you need to minimize errors.
The other issue with plain text accounting software is most of it only flags errors after you 'compile' your books (or, more properly, run them through some sort of command-line tool), which is far too late to make data entry convenient. (Some of them have web-based tools, like beancounts "fava" package, that act more like Gnucash...but at that point the term "plain text accounting" loses all meaning IMO, you're just using another client, so why not use a better one?
Gnucash has a lot of cruft and definitely feels like it was written in 2003, but it does address this issue and provides the basic input validation you need to minimize errors.
The other issue with plain text accounting software is most of it only flags errors after you 'compile' your books (or, more properly, run them through some sort of command-line tool), which is far too late to make data entry convenient. (Some of them have web-based tools, like beancounts "fava" package, that act more like Gnucash...but at that point the term "plain text accounting" loses all meaning IMO, you're just using another client, so why not use a better one?