I'm not familiar w/ bitplastic. I couldn't say if it's a scam or not. But it must be set up as a fiat type of prepaid card... meaning you'd need to send your BTC somewhere to preload it in dollars or euros. Basically a private buyers service that then loads your card with fiat. This is a runaround (in some sense) but there is no way they're doing it as an on-the-fly conversion, and it probably means sending your BTC to a questionable anonymous account first. Personally I'd rather just sell BTC on a legitimate exchange when I want to.