If you have the #64 space, ttd breaks it down into 2^32 ranges (I believe), so ranges are randomly selected and assigned to users; so it will take 2^32 searches to touch the entire 64 bit range. The other pool breaks the entire range down where users search 2^19 ranges (considered 1 round, spread out over the entire #64 range) and search 2^32 keys within each range. After the 2^19 ranges have been searched, the next start range is shifted by beginning range 8000000000000000 + 2^32. Next start range would be 8000000000000000 + 2^32 + 2^32, next start range, etc.. In this way, every space of #64 is touched, every round. It is merely a different concept versus ttd. I understand you have a lot invested with ttd's pool, so of course you will want people to join it where you have a large majority of ranges searched.