Other open-source hardware wallets (altcoin wallet, not bitcoin only) have few users and less attention, making them less secure.
Having less attention doesn't necessarily make you less secure. In fact it may be the exact opposite.
1) I need a secure wallet to store altcoins, and I believe Trezor should be the best choice. It is the most famous among open-source wallets and has the least possibility of having a backdoor. Even for Trezor, the number of users is only slightly over a million (1M+, according to the official website).
Some years ago (before going Bitcoin-only) I bought a Trezor One and I used it for some altcoins. I was good. I haven't been informed though lately, because since 2020 I am bitcoin-only, so I don't use this wallet (or any other altcoin wallet).