Pros: These *are* indeed interoperable with the older units

Cons: none so far - they work fine

Overall Review: After more messing with the configuration program, I was able to get the older units to communicate. I apologize for jumping the gun. User error :^(

Pros: The two units in the kit communicate with each other just fine.

Cons: Purchased this kit primarily because I have 4 older ZyXel homeplug adapters, the 200Mbps ones, and the information on the product claimed: "Backwards compatible with 500Mbps and 200Mbps powerline adapters" THEY ARE NOT COMPATIBLE!!! I tried with and without encryption - the old and new units do not see each other.