I have tried both the 901 atty and the 510 atty w/ adapter (using right now) I like both of them. Both of them work just great on a KR in my opinion. I think the 510 produces just a tad more vapor as I think it may not burn quite so hot as quickly. That's my personal observation and theory.
By far my favorite combo, and it is fabulous for making homemade
mods because you can grab n-type (or m-type if they are out by the way) connectors at any shack and build your little heart out - and Cartomizers, 901s, and adapters will screw right on
Take care,
- Hap