I would avoid Coinbase. My experience is that BTC purchases with them take 5 days. You don't know what BTC value will be in 5 days. If the transaction is favorable to Coinbase the transaction goes through. If it's favorable to you, (a lot of BTC per $), then they say you've been flagged as high risk and cancel it at the last minute.
That's unsubstantiated.
I've read on reddit of people buying BTC then having it delivered even in a rising market. However, I do question there business model.
It's supposed to be buy low sell high, not the other way around. Probably heading for bankruptcy.