Did you ever try it in p2pool
Yes, see the review linked in OP.
or with a high diff share?
Yes, "vardiff" works on BTC Guild with this miner.
After some very helpful advice from p2pool's author and #p2pool channel, it appeared to start working. Then Strange Things Happened. The miner and p2pool both started reporting very odd values for everything from hardware fan temperature to software share difficulty on the pool side.
So, it does not work with p2pool. right?