Well, I have no idea what the differences might be between Li-Poly and Li-Ion. I did do a test though: I have the $9 replacement battery which I discharged and fully charged through 3 cycles....and I have the original battery which runs fine in the Zaurus from new...and was also fully charged. I ran each with a microdrive holding a video file, overclocked the cpu to 624, and had the brightness on max. Each ran for an hour on my kitchen microwave timer, one battery was 50% depleted, the other 48% (I forget which battery was just 2% better).
When the replacement battery was new it needed a few deep discharges and recharging to "condition" it fully, otherwise all was perfect.