You’re not alone. Nobody really knows how there devices will work with the new APIs and App. Hell not even the consumer knows which app to use and which does/doesn’t work. I’m still waiting (for weeks now) for the Hub connected documentation to be released. I at least expected the other two to work, but oh well…
Personally I’d stay away from the groovy and wait for ST to get there new documentation and system ready. I’m also not doing any work on my DTHs and Smartapps till I know how to support the new app. But thats my personal opinion.
Groovy: works with ST classic. Not with the new Smartthings (Samsung Connect) app. At least what I heard from some people that tried custom devices with it.
Samsung connect: Probably only works with the new app. Has (for now) a pretty small user base, since ST has to transfer every ST user account to a Samsung Account before they can use it. And if you’re right the IDE doesn’t even work 