G2A (and most other key resellers) primary method is keys, it's kind of in the name. I've never been sent a gift through them just keys, I'd doubt it's their biggest system in use (and obviously won't be a thing for anyone going forward).
And Valve will never stop using keys. Always kind of amuses me that Humble, GMG, etc are put in one basket and G2A n CD-Keys are put in another. Both sell you steam keys and email them over to you to input into Steam just one of them you get Russian Borderlands and the other US Borderlands. Can't be having people using that globalisation against the publishers though. Instead you get all this "G2A steals credit cards" stuff which is so grounded on reality all you ever get is likes of Devolver (a publisher with active interest in using globilisation for own gains) tweeting about it, whereas I'd imagine if there was any actual evidence on that side of things then G2A wouldn't be long for court, theft n fraud are pretty serious offences. As it stands nada, but Valve have been in legal bother with US govt, EU govt and Australian govt for various dodgy practices they've directly or indirectly been involved in.
I like them for buying games from n all, but Valve are extremely anti-consumer when they think they can get away with it. You may notice the US one is relating to gambling, the EU and Australian ones are anti-consumer activities by Valve. Incidentally the EU one which launched a few months ago is related to region blocking which this latest change seems to maybe be a slight response to but given EU and EEA covers a relatively broad economic range (for example I'm UK, but G2A is Poland and Polish games are generally cheaper).