OK, I've just loaded up and configured DSLStats. If I look at the dslstats.ini file, I can see the details of my router and so on.
This is the Event Log:
13 Mar 2016 12:10:04 Configuration files stored in C:\Users\Brian\AppData\Local\dslstats\
13 Mar 2016 12:10:04 Snapshot folder is C:\Users\Brian\AppData\Local\dslstats\
13 Mar 2016 12:10:04 Average error data reset
13 Mar 2016 12:10:12 The configured modem/router is Billion 8800NL <-- this is actually the 8800AXL which works in the same way
13 Mar 2016 12:10:40 Config files moved from C:\Users\Brian\AppData\Local\dslstats\ to C:\Users\Brian\AppData\Local\DSLStats\
13 Mar 2016 12:10:45 Recording started
13 Mar 2016 12:10:47 Incorrect login name or password
An incorrect login name or password was supplied
13 Mar 2016 12:11:14 Recording stopped
13 Mar 2016 12:11:30 Recording started
13 Mar 2016 12:11:36 IP address is now [redacted]
13 Mar 2016 12:14:28 Sample rate set to 60 seconds (required value when MyDSLWebstats option is set)
13 Mar 2016 12:14:30 MyDSLWebStats validation check failed
Closed the program and it looks as though the changes are still present in the dslstats.ini file.
Restarted the program, and once again the settings have been blanked and will need to be re-entered. It looks like it is blanking the settings when I start the program. I've searched my hard drive in case it's pulling the file from elsewhere, but there is no other dslstats.ini file to be found.
The downloaded .zip file doesn't contain the .ini file, so I presume it is generated when the program is first run?