There are a couple of methods to use with Neinzul (and this is by no means an exhaustive list):
1. "Rampage" - Use them like autobombs, is the essence of this. Get a couple space docks with a couple engineers, and tell the space docks to produce ships on FRD, and give them a waypoint that's at the planet you want to get to. Ships will build, go off on FRD, and as soon as they see an enemy they'll start attacking. You don't need to worry about losses really, because they're so fast, and so easy to reproduce, and they're relatively tough. Do not build a regen chamber anywhere, otherwise the Neinzul will retreat and end up on your planet and just sit there, and you'll be wondering why you're not spamming Neinzul anymore. I'll use this method if I'm running a multi-planet start and have the resources to blow.
2. "Mixed" - build a Neinzul Regen chamber on your most forward (or most likely to be attacked planet), and rally all your produced Neinzul to that planet. Group them and send them on attacks, and when they get to 30% health (even if they're on a nearby planet without a regen chamber) they will retreat to the regen chamber, and will go on FRD on that planet when they're done healing at the chamber. This is the method I'll use if I'm on a single-planet start, and the Neinzul were my starting ship. It keeps costs down (especially with the auto-retreat) and makes for an effective defense as well, since you'll already have a pile of Neinzul retreating in front of any large AI counterattack.
3. "Cold Storage" - for minimal micro, you'll want to unlock Mk2 transports (mk1 transports will work, but not recommended). This would be for somewhere mid-game, when you want to make a pretty far deep strike using Neinzul. Just pile all your Neinzul into the transport regardless of what their health is (only works effectively with mk2, since it heals the neinzul instead of just halting their attrition like the mk1), and then send them off to attack. Chances are you'll want to scrap any regen chambers you have on your planets while this is happening, because the neinzul will never make it all the way back, and may end up angering a lot more AI ships than you'd want during their retreat.
The third method is going to be the most micro intensive, the first one requires no micro past changing the destination on the factories, and the second one requires no micro past what normal ships would require though it does need to be kept in mind that you'll never be attacking with a full force. Honestly, it would be really nice if the main fleetships had an option to turn on a "retreat at x% hitpoints," (MRS used to have space tugs for that, but those never worked) but that's probably bordering on making it too easy for players to avoid losses.
