Well have had prepaid at the abode for 2 years now I think and some of the stuff I have noted is as below.
1. Do not buy lumpsum amounts like 10k or 5k at a go. These attract some tax above 1000 or something like that. Kenya Power can confirm. Small amonts in the region of 500 -1k will keep you away from that tax. Also there is a tax that is paid in lumpsum and its not split up into the different tokens bought. Again I have no details.
2. The amount of power you get for a given amount of money paid is not constant. I have no idea how they calculate but 2 people spending the same on a prepaid token will recieve vastly different no. of units.
3. It is much easier to monitor your consumption. My house consumes about 10kwh per day n average. Most consumption is at night and I believe lights are biggest culprit. Even fluorescent tubes don't help.
4. I think the contractor was just lazy. They are supposed to be in your house not on a wall outside.