I bought a BRM Flex-Hone, 1" diameter, 180 grit. I've used it to clean up the inside of seat tubes so they don't scratch up the seatpost. They are actually a little larger than the stated size so 1" works well for a 27.2 seat tube. Lubricating it with WD40 occasionally while honing makes it cut smoother and last longer.
It's not a necessity but nice to have and it does a good job and it seems like it will last awhile.
Note:
According to the sizing information it seems 1 1/8" would be the correct size. I also purchased the 1 1/8" and it seems too tight - but it might work. 180 grit leaves a nice finish and doesn't cut too slowly.
https://www.amazon.com/25mm-Flex-Hon...nder+ball+hone