I had a K-r and yes I think it's a good camera to learn on - if you will stick with autofocus lenses like the ones that are included in this package. It's well made, very capable, and the sensor can record some very good images. You can also get really good results if you shoot in RAW and post-process later, as there is a lot of good dynamic range and color information on the files - it really isn't that far off more modern sensors in that respect, despite people saying they see "much better" image quality from the newer sensors. From the K-r/K-5 generation until now, the gains in image quality form the sensor have been incremental.
I had a lot of fun with it when I had mine - sold it for the K-S1 because I do use manual focus lenses a lot and the K-S1 has a much bigger and better viewfinder. I also used it under artificial lights where the K-r and the original K-5 struggle to focus correctly. If it wasn't for those two things I would have kept it without any questions, it's a very good camera and incredible value at the price you found.
But the truth is, any Pentax DSLR will be a good tool for learning and has its advantages and trade offs, even some older ones. I learned most of what I know on a K20D which is a more advanced body (a lot more controls) but an older clearly less capable sensor. Well, at least I learned the technical side of photography, now I'm still trying to learn the photography part, if that makes sense
Good luck and whatever you end up with, try to focus on having fun!