No, they aren't
Most fandiscs are created to further milk the fanbase by adding more fanservice and cram them with utter, meaningless crap that usually has little to no meaning for the original story itself; i.e. stuff most people won't care about, but still exists to please the hardcore fans, hence the naming. There are, of course, exceptions. Some of these actually either expand on original plot, act as true endings or "after" stories, adding new content. They are very rare, though. If story is coherent, most developers aim to include some sort of an explanation to events within the original game, instead of creating fandiscs.
The whole meaning of the word "fandisc" got warped nowadays anyway; back in the old times, fandisc meant more of a treat for fans, packed with various goodies from the creators - unique wallpapers, system applications, minigames, short stories (novels), arranged soundtracks and sound dramas, along with discount coupons for their future games etc. It was only later, when fandiscs began to become more self-contained additional stories, expanding on the game's universe (but not necesarilly the game's storyline).
There's a reason why fan translators ignore majority of fandiscs; they aren't worth translating.
Art by Oyarii Ashito and pleasant atmosphere. It's okay in overall, but still remains the weakest of LittleWitch vn's. If you want the really good stuff, you have Quartett!, Romanesque and Rondo Leaflet (which is prolly their best game). I've seen people speaking well of Sugar Coat Freaks, but can't say anything myself, since I haven't played it; it doesn't really seem that appealing from my perspective, although it prolly has the most up-to-date Oyarii's art, which is preety much the artstyle he's using nowadays; I myself prefer his older works, which were incomparably ahead of his current artstyle.