So far these Via VT6421A seemed to work OK for me. Detecting modern SATA drives and booting fine for them on Pentium/MMX PCs, as opposed to Silicon Image SIL3114 SATA controllers which detected the drive, but didn't even try to boot from it for some reason. Same SIL card works fine on Athlon XP system, so I guess it's something to do with BIOS + card combo...

Only problem with my VT6421A cards (apart from placeholder BIOS chip it originally had instead of real thing) is that it doesn't have connector for HDD activity LED

While SIL card has one. And that annoys me 😬.
So I looked for VT6421A datasheet and was lucky to find what I was looking for!

SATALED pin on VT6421A sounds what I was looking for.
On my card that pin is connected 3.3V from on board voltage regulator via R31, 4.7k ohm SMD resistor.

So I desoldered the resistor and soldered 47 ohm resistor, not related to 4.7k ohm it had before, it's for HDD LED and since power source is 3.3V you can't go too big or it won't light up. Technically it should be even smaller than 47 ohm but I wanted to start safe.

On the other side I soldered standard 2 pin connector and using a bit of snot (hot glue) I fixed the connector and wires on the board

And it worked! It blinks when there's activity on SSD that's connected to it. I don't know if it'll work for IDE port. With the pin being called SATALED... but there isn't IDELED pin so who knows 🤔. I have no need for it's IDE port so that part was not important to me.

So if someone is also annoyed by lack of activity LED connector on these cheap cards there's a quick fix for it 😀.