It's mainly for convenience. Much easier to manage tags in flac than in wav. Playing flac files on PCs or smartphones is very similar to playing mp3 files. Not so for wav files where one doesn't have the ability manage genres, artists, albums etc.
The other advantage is that there is some lossless compression with flac so it's a little easier on hard drive space and limited portable device storage.
Haven't had a chance to test the other product yet & I'd prefer to stick with Spin-it-Again. It would be great if you offered flac support.
btw, more and more websites like https://www.hdtracks.com/index.php
are appearing. They offer flac.
Finally, from my point of view, it's a lot of work to make a good digital copy of an analog source like an LP. I don't want to diminish that hard work for the sake of a few megabytes of space.