So to answer your question...yes, they are real.
The prices currently are around $17,000 to $22,000, depending on the conversion piece.
There are three conversions that I know of.
The cheapest is the registered receiver conversion. These are approximately $17,000 or so.
The second is the registered sear. These are about $20,000 or so.
The most desirable is the registered pack. These are the highest at approximately $22,000+.
People, even Norrell owners confuse the sears with the packs. The packs are the most desirable and will probably have the greatest longevity of the conversions because the internals can all be replaced, and there is zero stress on the pack.
The sears are often confused for the packs because the sears often are in a pack, and the packs have a serial number serialized on the packs. When people talk about the 'packs', they're referring to the trigger box, itself.
It's the same scenario with the HK sears that come in packs and the DLO trigger packs, if you're familiar with how those work. When you have a sear gun, it's not the pack that is registered, even though someone wrote the serial number on the pack, rather, it's the sear that is registered. This is an important distinction because with a registered sear, you CAN replace the sear, but not the trigger box; whereas with the registered pack, you can replace the sear, but not the trigger box.
The conversions are more desirable because you can take any currently produced 10/22 and convert it to run with the registered conversion device. With the registered receiver, you're stuck with that 10/22.
I'm a collector, not a gunsmith, so I don't know what goes into converting the 10/22. But based on my conversions with knowledgable smiths, it's not that difficult. Most importantly, it's legal to do, provided you own a registered conversion piece.
As for issues, such as bolt bounce, reliability, etc...know that most 22LR MGs are notoriously unreliable. They require lots of maintenance and gunsmithing to run reliably. Also, they require lots of cleaning. 22LR, especially if you shoot the cheap lead exposed ammo, can really gunk up the mechanisms.
Finally, I hate 22LR MGs of any sort. They're fun to own for a few sessions, then they become a pain. The reason is the ROF and the pain of reloading the mag. They just don't provide enough of a 'bang' for the effort put into running it. Have you ever tried loading 30-50 22LR rounds into a magazine? It's more effort than loading 30 into an AR. Then imagine the entire magazine zipping out in two seconds. Rinse, repeat. Gets old real fast.
Disclaimer: don't rely on my advice above. Do your own research.