Both encrypt in the client, so neither provider can read what you share. The differences are whether you need an account to create something, and whether you can ask someone for a credential instead of only sending one. Including the parts where Bitwarden is ahead.
In short: if you already pay for Bitwarden, Send is the shortest path and there is little reason to move. Erseni Vault is worth a look for two things: nobody needs an account to use it, not even you, and it can request a credential from someone else, which Bitwarden Send cannot do at all.
Every line states what each tool does, not just a tick or a cross. Where we are behind, it says so.
You already use Bitwarden. The account, the apps and the habits are in place, and Send costs you nothing extra to adopt.
You need to share files rather than short credentials. Bitwarden handles size far better.
You want a vendor with a long track record and published third-party audits. Erseni Vault has neither yet.
You need native mobile apps or a browser extension rather than a web page.
Every share tool solves the same half of the problem: you hold a secret and want to hand it over. Day to day the need often runs the other way. You need an API key from a contractor, a login from a client, a password from a colleague, so you ask by email and the answer arrives in plaintext in your inbox. Nothing has been gained. Erseni Vault turns that around: you create a request link and send it to that person. Their browser generates a key pair locally, encrypts what they type against it, and sends only ciphertext to us. You alone can decrypt it. They need no account, no app and no understanding beyond filling in a field. This is the difference worth switching for, and if you never need that direction, Bitwarden Send is a fine tool to stay with.
We compare against public documentation and source code, and we say when we have not verified something ourselves. Products change: if a detail here matters to your decision, check it at the source before you rely on it.
Bitwarden Send FAQ Covers the account requirement for creating a Send, expiry rules, file Sends on paid plans and the client-side encryption model.
Bitwarden on GitHub The self-hostable server. Not every part of the commercial product is covered by it.
Erseni Vault source code The cryptography component behind both sending and requesting, readable under the AGPL.
Send a secret or create a request link right now, without an account. The comparison above is easier to judge once you have used both.
Free tier, no credit card, no sales call.