The streamers seem to be some of the more honest "influencers" acting as entertainers. At least ones I follow (there are many subgroupings within) will disclose if they have any special connections or contractual obligations (can't show this cutscene or boss fight prerelease), sponsorships, or even if they just received a free copy.

I would advise treating unaffiliated middlemen as scammers like those offering jobs for money. (If there is some affiliated group of streamers and they handle communications that is fine.) If you want cheap marketing releasing some free copies generate no to marginal expenses.

It is respectful to all involved - you are giving away a few potential sales in exchange for a potential larger market, they can give it a fair shake and let people know what they think.

The viral effect can be real but it seems to depend on its own merits even if the "merit" is a gimmick like being hillariously glitchy.