BlueMooner: I just got a free trial of prime. Two questions:

What happens if I go to redeem a game I already have on gog? Will gog stop me from redeeming? Will Prime stop me? Will the key be wasted? I'm basically wondering if I have to check every game first before redeeming to make sure the keys aren't wasted, or is there some safeguard that will stop me from claiming gog games I already have.

Some of the games are on prime itself. When my trial ends will I still have access to those games or will the prime "launcher" only work with an active membership?

BlueMooner: That's precisely why I was asking.
That game is likely either Luna or Epic release I believe.

I don't use either one so not sure, but I imagine you need to use the Luna app from Amazon (I think lol) to play any of the games marked as Luna and Epic app for those marked as Epic, though I think some of these only need Epic to install. But all games that Amazon lists under the free games tab of the Prime Gaming page is free.

I also believe the Epic versions require linking your Epic account to you Amazon Prime account. I'm curious about how Luna works and I may download it on my Windows 10 SSD to find out maybe.

Only the GOG version has true offline installers, meaning no internet connection required.

[Note: It's my understanding that Luna is an Amazon app, but I don't recall where I got that info, so can't 100% confirm that.]
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Update:
I logged in to Amazon Prime and the games I thought were Luna, it says Amazon Games app. Either they got a new name or Luna was something else and I mistook it. Maybe someone can confirm that.
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BlueMooner: I just got a free trial of prime. Two questions:

What happens if I go to redeem a game I already have on gog? Will gog stop me from redeeming? Will Prime stop me? Will the key be wasted? I'm basically wondering if I have to check every game first before redeeming to make sure the keys aren't wasted, or is there some safeguard that will stop me from claiming gog games I already have.

Some of the games are on prime itself. When my trial ends will I still have access to those games or will the prime "launcher" only work with an active membership?

Oriza-Triznyák: They are giving away the outdated version of Hero's Hour. Also they removed the Rogue RealmsDLC from the Gog store .
You can only redeem it through purchasing the Deluxe Edition ( 70% off if you own the base game )

(ø,ø): How is it outdated? Do you mean the unnamed patch that came out on Steam just 2 days ago?

wyllow: Maybe "Please note that saves from the base game are not compatible with the Deluxe Edition."

(ø,ø): Both the standard and Deluxe Edition of Hero's Hour is updated to version 2.7.1. That the saves from one isn't compatible with the other is most likely just because the Deluxe Edition has more content.