There are a couple of things to know about this product. First, the OEM Canon NP-E3 Ni-MH battery is 1650mAh. This Delkin Devices DD/NP-E3 Ni-MH battery is 2200mAh. This Delkin is much less expensive than the Canon and both are rechargeable in the OEM Canon NC-E2 charger.
When Delkin Devices ships this battery there is a note enclosed. It states, "Out of respect for Canon's Intellectual Design Property ..." the Delkin has only a single twist lock, not the double locking mechanism as found on the OEM Canon NP-E3. Okay, fine.
What I did was remove the OEM Canon locking device (two little screws) from the old, dead Canon NP-E3 and install it on this Delkin. Hence, no worries about the locking device, not that there would be, anyway.
Before I used this battery, I ran it through a "Refresh" discharge/re-charge cycle on the Canon NC-E2 charger, and now it is working perfectly.
I have not used it enough to compare it side-by-side with the OEM Canon.
On the EOS-1Ds (11.1MP), I got 225 images (on the RAW + small JPEG setting) out of the OEM Canon NP-E3, plus lots of other usage (sensor cleaning ... firmware download, etc.). Right now I don't know how long this Delkin will "run," because I have not yet used it long enough, but it is performing perfectly. No problems, whatsoever.
I fully understand why people want to stick with OEM Canon. However, I'd argue that you can use this well-made, high-quality Delkin replacement battery without fear.