A specific relay is one of the factors, but the most important difference is that both parties use temporary keys, ensuring a certain level of forward secrecy.
nostr:nprofile1qqswswmx4rkj6d7q05dtafhpkqq2z42fc62s37jvtp642m2jkpfxc2cpz3mhxue69uhhyetvv9ujuerpd46hxtnfduq3wamnwvaz7tmwdae8g6tn9ehx7um5wgcjucm0d5q3wamnwvaz7tmxd9k8getj9ehx7um5wgh8w6twv5nrafuh nostr:nprofile1qqsdwqn6l9zwepuv7nq09zp27el05y88cdvcyy0pal2mr5mcmtcvcfgpz4mhxue69uhkummnw3ezummcw3ezuer9wchszxthwden5te0wfjkccte9eekummjwsh8xmmrd9skctcpzdmhxue69uhhwmm59e6hg7r09ehkuef03lvp44
afaik, the main thing about a secret chat is that your messages will be sent and received to/from one specific relay, isolated. based on my experience since the relay is limited and specific the performance is better as well.
Discussion
GM
Use nostr:npub1tm99pgz2lth724jeld6gzz6zv48zy6xp4n9xu5uqrwvx9km54qaqkkxn72 as your messaging app when you can.
You are in control of your keys and your messages, not a company or the government.
Convince your F&F, this will pruplepill them.
Zapping sats will orangepill them.
THIS IS A WAY.
nostr:note16jgrym2teg4rrwcv6ds2cw8erjlydp3euhra56yngkuejtfp8uws77myg9