Every model requires a bespoke firmware image. It's probably a good thing that the vendor firmware upgrade page failed to allow you to install OpenWrt built for another model... if it had allowed it, you probably would have a brick on your hands.
Yes, the 620 and 630 are supported by 24.10 (still in RC phase as I write this). But the 625 is not supported by any current version, including snapshot.
Ok, that is a shame. The 620 and 630 for some reason are much more expensive than the 625. Any idea if it would be supported in the future? The 625 is $100 USD less than the 620 and 630.
I'm pretty new to OpenWRT, but I'd also really like this device to be supported. Which of course doesn't mean that I am expecting anyone to "waste" their time on it. This link contains internal pictures and documentation of the WAX625 from the FCC, which might be very useful for anyone trying to figure out how to get OpenWrt working. It was a bit hard to find the device on their website, so I thought that posting it here might help someone.
As far as I know, this device might become unsupported by Netgear since certain versions have already reached their EOL date according to a Netgear pdf. This means that there might be hope for more people wanting to work on this in the future.