That thing is ludicrously expensive.

That's because it was purpose built to be a ZIL (ZFS intent log) in large production fileservers. Cost was less of an issue than performance.

Still capped at 4GB you can get other PCIE RAMdisks with higher capacity which are cheaper not sure if they'll perform the same tho...

Well, for starters this thing is almost 10 years old now. So comparing it to something developed in the last year isn't really fair.

That being said, where's this list of RAMdisks, in a PCIe form factor, with a capacitor/battery backup, and hardened Solaris drivers? I don't think I've ever run across one.

Importantly it's not SATA.