kr808d-2 is an e9 PV, so compatible with GS. The kr808d-1 is a different cartomizer PV, and I don't think is compatible, but does get rave reviews, and is considered about the best carto PV on the market.
I started with GS too. It was ok. The passthrough was killer...until it started burning up my cartos. The e9 batts were less than ideal. Wasn't fond of the flavors, although the vanilla and mint were good.
I switched to a 510. Fantastic, and MUCH better than GS, and for about 1/4 the price. The regular batts were not great, but they can be extended with a PCC. I got a bunch of mega batts, which for the money are good...last about 1.6x a regular, and a bit more punch.
The 510 atty, however, is really good, and most bigger batt mods use it for that reason. The 510 is probably the most supported PV system of all the vendors on ECF. And there are adapters to switch to kr808d-1 cartos for the 510 batt. That might not be the best idea since the kr808d-1 batt is far better than the 510 batt. However, I am now using a Bartleby with 510 atty. When you beef up the battery capacity with bigger batts, the 510 becomes truly excellent.
I would say the 510 has the most info here too...but with the kr808d-1 a close second. Both are great systems, for different reasons. Both very affordable to get started with, especially compared to the GS. After you get one of these (or both!), you may find that the GS gear gets put into storage. The E9 is not very well supported, certainly no where nearly like the 510 or kr808d-1. But when we were first breathlessly looking for the perfect first PV, GreenSmoke seemed to be the one really trumped up in the vids and ads. And we didn't know about ECF. So we bought the GS at $150 a kit...or Smoking Everywhere or NJoy or whatever late night radio ad told us to buy. Live and learn. I learned a lot about PVs from the GS, but for now anyway I'm a 510 with a 14500 batt mod, and I love it love it love it...for now....
I recommend the 510 for ease of adding your own juices, and potential to really hot-rod it with cart mods or batt mods. But either that or the kr808d-1 will be worlds better than the GS.