I'm working for a journalistic organization that cooperated with Google to create one of the graduated Jigsaw projects (Investigative Dashboard).
We were considering using Project Shield relatively recently (as in, some time this year), but at that time, the info about how it actually worked was... well, non-existing on their website. IIRC, their SSL support is also fairly new, which made it pretty unusable until very recently.
Interestingly, I've never looked deeply at what Project Shield does under the covers but I know what all the underlying technology "must" be. The main difference between GCLB and Shield, is that Shield is a free service (operated by a different group, as already mentioned) explicitly for those at risk of censorship.
As another poster indicated, if you want someone to terminate SSL for you, you're going to need to hand them a key. We encrypt ours at rest, provide the same security and care to your secret material as we do Google properties, and as you can see with our Customer Supplied Encryption Key support for Persistent Disk and GCS, we care a lot about letting you control access to your data. If you don't mind me asking, to whom are you comfortable uploading your keys to?
Disclosure: I work on Google Cloud, so I'm actively trying to take your money in exchange for our services.
Keyless SSL is a great thing for people who really can't convince their auditors that it's okay to share their keys. But, it has its own problems like:
> Note: Keyless SSL requires that CloudFlare decrypt, inspect and re-encrypt traffic for transmission back to a customer’s origin.
That's not particularly different (to me), but I have a different threat model. Again, it comes down to what scenarios you care about and what you're comfortable with in exchange for <something>.
Even initiating tons of sessions is likely to mean that the key server is going to be busy. But if you're really concerned with sharing you key with us, I agree CloudFlare's Keyless SSL provides a real service that does a lot for you without handing the key over explicitly (you just have to keep doing your part).
We were considering using Project Shield relatively recently (as in, some time this year), but at that time, the info about how it actually worked was... well, non-existing on their website. IIRC, their SSL support is also fairly new, which made it pretty unusable until very recently.