Now, these might be bugs, or they might just be me completely failing to understand how riot starships are meant to work.
Firstly, all of the riot starship mkI modules say that they can only reduce engine health to a certain amount - 25% for the laser, 40% for the machine-gun - but I've definitely seen mkI Riot Starships leave enemies completely immobilised. I assume this is because of the guns mounted on the starship itself, rather than the hardpoints, but I don't know if it's intended behaviour - what's the point of limiting the engine damage the modules can inflict when the ship's own built-in guns ignore that limit?
Secondly, these completely immobilised enemies seem to be impossible to grab with tractor beams, which is a pain when I want to tow them through a wormhole to their doom. I think this is a slightly misbehaving feature - it makes sense for defensive tractor beam turrets to ignore immobilised foes, since they're not going anywhere, but I don't know if that smart targeting should have been carried across to mobile tractor platforms like the riot starship.
And, an aside - which module types do people prefer? I'm currently using 4* machine gun, 1* shield, and either 1* tractor or 1* riot shotgun depending on whether I want to capture ships or incapacitate them. All the medium hardpoints seem to have their niche, but I have no idea whether lasers or machine guns are better.