is the DIY variant secure, who has the experience ?
I can't comment on that particular video or the software he uses, but the Blockstream Jade is safe to use. It's an open-source and airgapped bitcoin-only hardware wallet. You can use it as a stateless signer via QR codes if you want. You have the choice to purchase the assembled device, which is very affordable and should cost you around $65, or you can purchase the individual components yourself and assemble everything on your own and build it from source.
The possibility to assemble your own hardware is a guarantee of the solidity of the project.
My own self compiled Jade works smoothly.
The main difference with the commercial solutions is the lack of a photocam, that downs allow to read QR.
Apart from that, I have no reason (to the best of my knowledge) to use a DYO variant using reliable sources.