Does using multiple hardware wallets (w/o seed) make sense?

[crwth]

What I initially thought of this is something of a Decoy Wallet. Like, if you were to be physically attacked or harassed into giving up your holdings, this would be a solution: having multiple hardware wallets.

Now for the seed, I don't think it's recommended to have no seed backup. If the device fails, what would you do? Maybe it's better to split your seeds with Shamir Backup ^IIRC. It will do the job for you.

[dkbit98]

I’m thinking of using multiple hardware wallets (e.g., 3 devices)

This is overkill for most people.

1. Is using 3 hardware wallets (with seeds only on the devices) a safer option than seed + passphrase? Are there long-term risks with relying on multiple wallets (e.g., hardware failure, tech obsolescence)?

Safer for what exactly? Nuclear war?? 
Multiple devices are only needed for multisig setup, and that is complicated and not needed for most people.
Only if you are high profile or crypto billionaire than using multisig setup with multiple devices could be a good idea.

2. How likely is it for an attacker to guess a passphrase made up of 4 words from the BIP-39 list? It seems like 4 words (2048 options per word) could be brute-forced in just a few days on powerful systems — how risky is this in practice?

Attacker is not going to guess anything if you are near devices, you are going to tell him passphrase sooner or later.
I would not use words from BIP-39 list for passphrase.

3. What’s your take on passphrases in general? How long or complex should they be to make brute-forcing impractical?

Don't use simple 1234 or overly complicated passphrase, and make sure to back it up, don't keep it only in your head.

[FinneysTrueVision]

Anybody who holds a meaningful amount of crypto has probably gotten paranoid about the possibility of their seed being leaked. Depending on your threat model, you might not be comfortable with leaving a piece of paper with your seed phrase lying around. Investing in a personal safe and keeping your seed there and the passphrase in a separate, secure location is going to be good enough for 99.9% of people.

Using multiple hardware wallets is less practical because they can stop working and need firmware updates on a regular basis. They also have most of the same risks as a paper backup of getting stolen, lost, or destroyed. I wouldn’t recommend this solution, but only you know what will work best for your specific needs.

[satscraper]

~

The safest setup involving three hardware wallets would be the multisig wallet with  2‑of‑3 quorum. Such setup becomes even stronger if at least one of your hardware wallets is BIP85 compliant. In that case, you can choose its SEED as the parent SEED to deterministically derive child seeds and use two of those child seeds for your other hardware wallets. Note that the child seeds are independent in the sense that they cannot be linked to each other.