The information about the percentage of interest is there on Kiva and you can set filters to exclude the more exorbitant ones. I seem to recall it is usually not interest charges that are high, just a percentage operating cut. Sometimes that was for legit reasons like the country involved was very challenging to operate in, others they just aren't very efficient.
What I didn't like when I was using Kiva was that some field partners practice religious indoctrination or at least have an agenda. So when your are funding loans you service you are funding and helping their religion. I had to rely on some third party lists that indicated which partners those might be, it was a pain but by loaning for projects like solar power and energy conservation I found that there were fewer religious orgs involved anyway.