Gleam is just a platform. It can be used equally by flakey "influencers", dodgy chinese dropshippers and legit stores.
Many people, including myself, have won competitions hosted on gleam.
As for PowerGPU, I would love it if ozb let you see whether anyone had ever won a comp hosted by a particular outfit, but they don't, and there's only 9 comps posted so the chance of someone from ozb winning one is low. But they appear to be a legit store with a reasonable social media presence and cross-promotion from verified accounts.
Does anyone even ever win these things? Of the countless "gleam" competitions I've entered I've never seen one winner.