Considering the current wild fluctuations in BTC, it concerns me that any company offering this service is exposing themselves to a significant risk even in a 24hr period from offer to acceptance.
Taking into account the past few months of volatility. They have to maintain significant assets to cover the extreme recent BTC price fluctuations.
Again, I don't know what their actual model is. But assuming they're selling BTC in the same time as you decided to 'lock' then the exposure is few seconds rather than 24 hours. If that's the way they do that, the risk is non-existent.
Price averaging is not practical when you have no idea how high or low it can go. As you can see by the 2014 charts, your guess is as good as anyone's.
The current situation is a clear example of problems the Bitcoin network will face in the future. Miners only continue to operate when its profitable. Bitcoin value will always be tied to operating costs of people, equipment, facilities & energy.
Will their be enough individuals running long term hashing power to support network transactions when mining is over? What will their operating costs be?
Will the system eventually transform into something centralized that will charge transaction fees to support operating costs? Which would be very similar to the banking system that we have today but without Government backing.
I'm not saying that price averaging is practical or safe, but it's yet just another way to protect yourself from volatility.
As for mining - no one can predict the future. But it's a self regulated system (less miners, diff goes down, profitable again). Also, I wouldn't be surprised if in future some of the large BTC related companies will be mining just to secure the network. If their profit is grater than loss on mining - it still would make sense (in financial terms) for them to do it.
And it will never be centralised (Central Bank style) as long as anyone is free to start mining or running a node.