I have been considering upgrading to the K-r, but this battery system seems very poorly designed for an otherwise good camera.
If the compartment is designed for AAs (the "ribs" inside suggest it is), why not just have contacts inside it for AAs, as with older Pentax cameras? Why a seperate (very expensive) little adapter? Or, if an adapter is necessary, why is it expensive and optional instead of included?
Or.. If it's not designed for AAs, and they are a secondary use.. Why not have space for a larger (higher capacity) "block" battery in there, and not the "ribs" to make it "AA shape"? An AA holder with a slightly different design could fit in such a space too.
Another missing option is CR-V3. The shape of the compartment looks basically compatible with them, but with the AA holder it wouldn't be. Leading me back to thinking the holder is stupid and there should just be contacts in the compartment compatible with AAs AND CR-V3s. Rechargable CR-V3s with their higher voltage (which may or may not hurt other cameras) would be ideal, and not give the
performance drop of AAs.