Thank you very much for your replies!
After I made my research and after I read and thought about your replies,
Here are my own conclusions about disadvantages of buying exotic hardware wallets even if they are cheap and even if they are open source:
1. Too few users means too few feed backs about how well it works. You just cannot rely on other people experience when choosing this wallet because there is too little of such experience to find on the internet.
Does the wallet have bugs? Is it assembled on high quality level? Are the chips inside it good? You don't know and often cannot find out. So you run the risk that the model itself is "bad". Not just your device but the model itself.
2. There are manufacturers who replace defective wallets only if you send them the defective wallet first.
I don't have answers to the questions like:
- Who pays for sending out defective wallet?
- What happens if you discovered it is defective AFTER you set it up with your seed, and cannot wipe/reset it?
- How long does it take to send it to manufacturer and get replacement?
But these questions must be answered BEFORE you buy the wallet.
3. There are some wallets which you can order solely from Asia. If you don't live in Asia yourself, it may happen that customs in your country is suspisious concerning parcels from Asia (I have heard it is so in some contries). Then they may unpack your wallet to check what is inside the package. And you may never feel secure if you receive the wallet that was unpacked.
4. Some wallets may have features which are not known to users and which are something really unusual and at the same time dangerous if you treat your wallet just like you used to from your past experience with other wallets.
An example that I found on reddit:
https://www.reddit.com/r/CryptoCurrency/comments/snryqo/warning_flaw_in_blockstream_jade_hardware_wallet/ 5. Some companies manufacturing hardware wallets are very young, small and have indefinite future. You never know how long their support will dure. May be the company will disappear tomorrow?
And yes, some manufacturers websites look like if the company were dieing and didn't care much about its product anymore. Though it continue selling it.
6. Some well promoted and great looking hardware wallets are not so good devices as they seem to be.
According to users experience if you succeed to find it on the intermet.
They still may be inconvenient and dangerous due to lack of proper support of their software.
7. A small manufacturer may not have enough financial resources which are necessary for spending them on creating proper security updates of device. So the device may be insecure just because manufacturer has no money to constantly make updates.
8. Well known open source brands are constantly checked by many independent checkers. Little known brands may be not checked at all. And if the first one who checks it is a hacker it could be very bad for users.
So an advice which I would give to myself:
I you want a toy and can afford it, then buy whatever exotic hardware wallet you like and play with it.
If you want a real thing and are serious about safety of your funds, then buy a well known and well tested model from a manufacturer whose business feel great.
What do you think guys?