Yes, much like my review of the main show, I'm over a decade late to the party here too. Now, on many platforms, the Specials of Suisei no Gargantia are called "Episode 14" and "Episode 15", however they do not fit those monikers when looking at the chronology of the main story. Special 1, focussing on giving Ridget some more backstory and depth (and some nice Ledo x Amy moments), would appear to take place quite early, probably being placed at some point around/between Episodes 4, 5 and 6 in the main season. Ultimately, it's the weakest of the 2 specials, as it doesn't really provide oroffer anything substantial.

If this was extra content left on the cutting-room floor from the main season, I can see why it was cut. Nice to watch, but ultimately no real substance. Could call it the epitome of a filler episode.

Special 2, on the other hand, is a different thing entirely. This one delves into Commander Kugel and Striker ending up on Earth, and how they "ascended to Godhood", leading to them having their massive fleet in the later episodes of the main show. It gives much needed character building on Kugel, and shows his thought process on making the fleet more "efficient".

In my review of the main show, I did mention how Kugel and his fleet was a fairly big unexplained "plot-hole", and here it is explained. It could be argued this special isn't a necessity to watch after the main season, but I believe this one really should have been put in as a flashback/world-building episode taking place around Episodes 11 - 13 of the main show. They probably didn't want to break up the action in those later episodes though, so cut it out.

Ultimately, these 2 Specials are both held up by the second. If I considered Special 1 as 6/10 "Fine" (watchable, but nothing important), and Special 2 as 8/10 "Very Good", the average here is a 7/10.
As one Special is an easy skip, while the other is bordering on a "must-watch", it's Mixed Feelings overall.