Unfortunately, you are unable to download your DigitalOcean snapshots and backups outside of the DigitalOcean environment. They have not made this feature available. There has been talking about making it possible but we have not seen DigitalOcean make any steps towards making this possible.
You can do a lot with DigitalOcean snapshots within their network. Create new droplets from Snapshot, restore existing droplets to snapshot and moving snapshot across data centres.
Here at SnapShooter we find that snapshots are an extremely powerful way to protect droplets and volumes. Recovering a server is extremely fast compared to restoring from an external source, network lag is very real when your moving GB's of data in a hurry (especially when uploading from a consumer ISP connection). We also value the importance of not putting all your eggs in one basket. We recommend to all our customers and DigitalOcean customers to also create off-site backups.
Here is our recommended a list of articles created by the Digital Ocean community to get you started.