This only applies to users who have set up shakers to work when the 'Screen is Off'. For example, this would include the functionality to wake the phone up (i.e. 'Turn Screen On'). If there are no shakers defined for this scenario, then there should not be any battery issues and you can disregard the rest of this post.
For users who have shakers set up to work when the screen is off, Shaker version 1.1.1 and up should provide a significant improvement in battery life depending on how the phone is used. Basically, if the phone is in a pocket, purse, or even face down on a surface, the app will allow the phone to go into its low power state when the screen is off, without impacting the functionality of the Shaker app. As long as the phone is allowed to go into its low power state, which is its normal behavior, there should be minimal impact on the battery from this app.
It is using the proximity sensor on the phone to determine when the device is in a pocket, etc. So, when the phone screen is close to any object at all with the screen off, shakes will not be detected. This same sensor is used by the phone to turn off the screen when you bring it close to your face while on a phone call.
There are a couple of caveats:
1) The option on the settings screen to 'Disable in Pocket' must be checked.
2) I have noticed that sometimes the proximity sensor does not do well in detecting proximity when laying flat on a hard or reflective surface. So, if you put the device face down on a desk, for example, there is a chance it will not actually detect it. It seems to work better when the device is face down on something slightly more malleable, like a piece of paper, a couch cushion, or something else that is not as hard and flat as a desk. This may vary from phone to phone depending on the sensor that is being used and how well that sensor is working.
As always, please let me know what you think, whether it is positive or negative, and especially as it pertains to battery use on your device.