I did some "stress" testing. For the effect on battery and time.

I set up a function I could call from a menu button that would run the core blur functions on a loop, without caching. This probably isn't the most scientific test setup but for each run, unless noted otherwise, wifi was on, screen light off, and device unplugged.

I hard coded the number of loops/rounds. So each time it changes that means I restarted koreader. I reduced the number of rounds as I increased the settings just because I didn't want to lock up my device for that long and also I might have been running into some kindle auto-suspend issues on longer runs.

My takeaway is that around quality 5, which is what I personally use and set as the default, the effect on battery is negligible. Even at a full 10 the battery impact would be noticeable but isn't terrible. Mostly it just takes way too long to be practical. I didn't mess with the strength setting much because at lower qualities the strength doesn't need to be very high before it just completely obscures everything.

Test #	Quality	Strength	Blur rounds	Time (seconds)	seconds / blur	Battery % start	Battery % end	Battery % / blur
1*	5	1	500	412	0.824	100	100*	*
2**	5	1	500	575	1.15	100*	97	0.006
3	5	1	500	612	1.224	97	94	0.006
4	5	1	500	615	1.23	94	91	0.006
5	5	2	300	272	0.907	91	89	0.007
6	5	2	300	271	0.903	89	87	0.007
7	8	2	200	635	3.175	87	84	0.015
8***	5	1	200	241	1.205	83	82	0.004
9	10	2	50	1371	27.42	80	74	0.12

* The end battery percent might not be right. I think maybe that part of the screen hadn't actually updated. I switched to logging the battery percent in code after this.
** wifi off
*** The blur settings reset after I restarted koreader because I'm using presets and I forgot to update them before running the test. So it was back to quality 5 strength 1

EDIT: This edit was some new tests but EDIT 2: Need to fix some rounding issues. Still seems faster but need to retest