It claimed users wouldn't suffer a performance penalty for using the service, but added it plans to double the Quad9 PoPs over the next 18 months.
They're both right and wrong.
You won't suffer a performance penalty on your DNS lookups, they'll come back nice and quickly.
But, the service doesn't support the EDNS Client_Subnet extension, so most CDN's will wind up geo-locating you to wherever the resolver you've hit is located. If it's a US DNS server that answer's your query, you'll get a CDN cache in the US even if you're the other side of the ocean.
IMO, it's a pretty big feature to be launching without on today's internet, and it's likely going to cause various CDN's lots of tickets from users/operators claiming that delivery is slow and they're being routed to machines in the wrong country.
The lack fo EDNS is deliberate - to preserve the user's privacy (so that they're not spurting your source subnet out to each authoritative nameserver you require records from). On the other hand, that "privacy" pretty much vanishes the second you use the received records to establish a connection to their servers, so *shrug*.
Definitely nice to see a new competitor to OpenDNS/Google pop-up, but I'm not going to be using them until they've got working ECS support in place. It's claimed that 184.108.40.206 does support ECS, but a packet capture on my authoritative servers suggests that either this isn't the case, or their using a whitelist of authoritative nameservers (which I'm not on).