No, they are not fine. Their design means that the router needs to know all possible extension headers to just be able to route the packets. Oh, and you also have to do offset-chasing in the hardware fastpath.
As a consequence, IPv6 with extension headers are just dropped by routers in the public Internet.
With one exception, extension headers are not examined or processed
by any node along a packet's delivery path, until the packet reaches
the node (or each of the set of nodes, in the case of multicast)
identified in the Destination Address field of the IPv6 header.
That seems like the opposite of needing to know all possible extension headers in order to route a packet.
The issue is that the extension headers can be used for nefarious purposes, such as hop-by-hop routing. So your fast hardware-based border routers might be EH-agnostic and transmit packets to your core network. And then a helpful Linux box that implements all of IPv6 in software would reflect the traffic right past your firewall.
Implementing the EHs in hardware is expensive, as you need to do conditional checks. So routers just drop them.
As a consequence, IPv6 with extension headers are just dropped by routers in the public Internet.