Apologies, if this subject has been beaten to death, but the search function on this forum is not very helpful.

Looking to replace the alloy seat post on my touring bike. Of course it's 30.8 mm, not the most common size, but do-able. I see the biggest selection for that size is carbon. Some cost $20, others cost $200. Presently looking at what's called 3K carbon.

Any education and opinions would be greatly appreciated, regarding reliability, warnings and any special things to keep in mind.

Thanks