Unfortunately, I have not been able to use the fleet battle, meaning I can't make any judgements about it or test the ships I create or download. Of the four times I attempted to play the battle mode, my computer had to be restarted, and the remaining two times, only one prompted a crash report. Not sure if it's a problem with the game, my computer, or both.
As for the ship creation? It's pretty well-designed, and aside from occasional fidgety placement of parts, it isn't too difficult to use., and is quite fun. However, some form of mirror option would be nice, as would the option to copy/paste adjusted parts. Descriptions and/or animations of the various weapons would be nice, since I can only determine what they do via the battle mode, which I previously mentioned that I can't access. When trying to upload a ship to Steam, the description stays in the uppermost line and gets lost off the edge of the screen, and it's a minor inconvenience to not be able to make new paragraphs.
EDIT: Since I am unable to make more than two posts, apparently, I will have to instead edit this post further.
The reason for Fleet Battle crashing my game, I've discovered, is putting my Neobliterator ship into a fleet-- mine or the enemy's. The mode works mostly fine with just official ships, though I have run into the same problem others have had where the ships become invisible. All of them, not just the ones currently in play. My other ship, the Twilight Shipkle, works in battle mode, but caused a glitch where all sound was muted, and attempting to surrender and quit caused the previously mentioned black screen/zoomed in problem.
The reason the Neobliterator doesn't work is, I reason, because of an error involving one of its parts. However, deleting parts in the editing mode isn't that convenient, since I have to delete all the connected parts and all their connected parts and so on just to get to one of them. It would be convenient to be able to delete parts without having to delete others, or at least deleting all the connected parts automatically by deleting their base.
Can't wait for the future, and all the wonderful goodies it'll bring!