I actually tried Coop a month or two ago, and just updated it, it's changed a lot since then, and I really like the new UI!
I also saw a message that I hadn’t seen in any other client, and I replied to it, though I’m not sure if the other person can see my response. That uncertainty is why I rarely use Nostr DM clients. Hopefully one day all the DM client devs can get together and agree on one or two protocols, haha