I was flipping through my Koronus Bestiary today, remembering how much I love the Eldar, when I had a thought. The books never touch on the Eldar Jetbikes (or the Shining Spears, obviously), which was one of my favorite upgrades for some Eldar units. Farseers and Autarchs could be killer on JBikes, getting extra Toughness, increased movement, and so on. Farseers could get around, and get their powers to key places with ease, while the Autarchs could combine some cheesy weapon options with said high mobility. An Autarch with a bike, a Powersword or Diresword, and a Reaper Laucher or Prism Rifle (I also love that the Shadow Spectres made it into the book) could get anywhere, deal tremendous damage, and really put the fear of the Eldar into their timid foes.

In the RP, though, is it worth it? Missing rules are no hindrance, with Children of Isha pdf or the DE bikes from Only War filling in fine, but does it just slow them down? One of the Eldar's greatest advantages is their preternatural agility, dancing around attacks that would spludge them, otherwise, to then kill their enemies with the same swift grace. Would the jet bikes JUST make them easier to hit, taking their fancy footwork, and putting it away, to leave them, or their bikes, getting pinged? I think that a combination of being mounted, coupled with the Auto-stabilized trait, would still allow the Autarch to wield his RL (one of my favorite Eldar guns), and fall back on the sword of choice if close combat appears, while still riding high, and Serrenon in LotE, or any similar Farseer, could be sick on a bike, too, but I don't know if the best reason they might've left them out was because it made the Eldar too easy to hit.

Opinions? Would Eldar in RT benefit from their jetbikes, or should they leave them corralled in whatever transport brings bikes to the front?

The Soul Reaver book is all about Dark Eldar, and on Page 139 there are rules for a Reaver Jetbike. As for the specific career, if you download The Dark Kin from the Rogue Trader Support Page then you can find an Alternate Rank for being a Skyterror as a Dark Eldar.

I'd consider using them for a running gun battle, maybe have the Explorers in a Chimera or Rhino while Eldar bikes dart in and out, wolfpacking them. Used properly, they make a great force multiplier, but diminishing returns come quickly (too many and they end up tripping over each other, and can't get out of range or into cover effectively.)

Against infantry, or anything largely static in movement, I'd use few to none, since they're just low-armor targets, and Eldar don't seem willing to sacrifice some of their own troops as a distraction unless it's a truly desperate situation.

I think they would work best in the massed battle system from (iirc) battlefleet koronus, as they would be too much of a threat to PCs on foot and too impotent against a competent armoured division with AA coverage (hydra tanks will shred jetbikes)

If you think of them as vehicles, then yes, they are little more than a hidrance to the elday. Light armor for vehicles can get them shredded. Personally, I think of them as something like highly mobine terminators. Small arms fire is going to go mostly ignored, and you are still highly mobile. The things to really worry abour are anti vehicle weapons, which would hurt them anyway, and sharpshooters sniping the riders off. Put a warlock on one in the squad and he can help up thier survival. The main thing is use them in a similar way as terminators: shock and awe. Sudden arrival, decimating suprise attack. Shining spears could take out that hydra battery pretty quick. The eldar are all about ambush and would likely be lying in wait, avoiding a long approach that gets them shot up, or using terrain to approach without being seen/shot up. If the initial attack removes the major threats to them, then they might stick aroun.d to finish things, otherwise then they would disappear back where they came. All in all I think riding a jetbike makes them easier to hit, but still much tougher than withoutt them.

The advantage is that Agility is used to drive (fly) a jetbike, as well as the jetbike's own incredibly high speed. While the DE book talks about the Reaver being super fast, it's not an expesially faster vehicle than regular Eldar jetbikes (I think). Maybe slow it down a bit and add some armour, as well as the expected weapon swap and removal of the bladesvanes.