I'm a huge proponent of SBI. I've run contests using shares as prizes before, and it helps when on-boarding new users to keep them active through those difficult first few weeks when getting noticed is extremely difficult.

I'm not sure where this notion that "it's a ponzi scheme" started, but anybody who looks at it and understands basic economics knows it fits none of the definitions of a ponzi scheme. SBI was started as an economic experiment on the blockchain, and its purpose (at least from my perspective) is to promote altruism and grow the community. I've delegated a portion of SP to SBI, and I've provided over 100 shares to various Steemians over the last few years. Some of them are still active, some of them are not, but it was my Steem to do with as I pleased, and I wasn't doing it to try and make money. It takes a LONG time to make ROI on a single share of SBI, and that's kind of the point: you're investing in the community, not yourself.