but what they are selling, just a piece of hardware with a software open-source light wallet installed on it?
what is the main difference between that solution, and same open-source software on some old laptop, that is not used for anything else, just to have access to your wallet?
why the Trezor is better (just asking, I do not think that it is not) from old laptop? and old laptop sitting somewhere is the basement could be not recognized as hardware wallet, or it would be harder than seeing Trezor as a wallet
what is a main Trezor advantage, in your opinion?
Trezor was one of the first HW wallet maker and it was their choice to not put a secure element within their devices. Their rationale being that the main attack vector is from the net, among various other stuff [1]. I saw this counterargument (by Ledger) years ago and thought that it made more sense[2].
Trezor is designed to not be vulnerable to typical malware and viruses as its primary purpose is to receive and sign transactions, so the attack vector is pretty small. I think their firmware is also signed so that isn't a threat.
I think your final question is about HW wallets in general. As said, the secure element will mitigate the attacks as mentioned. It really depends largely on your usage. Are you confident with handling air gapped storage? Do you want a bit more convenience while ensuring the same level of security? Do you want to save money on HW wallets?
Personally, I bought a HW wallet not because it's more secure (the threats are largely irrelevant to me) but that it provides much more convenience and portability than an airgapped wallet. Trust me, a hardware wallets makes everything smoother than starting your RPI up and realising your Electrum got corrupted again and having to find and type in the seeds again.
[1]
https://blog.trezor.io/is-banking-grade-security-good-enough-for-your-bitcoins-284065561e9b[2]
https://www.reddit.com/r/Bitcoin/comments/52x08n/is_bankinggrade_security_good_enough_for_your/d7odee4/