Somewhere in this forum I read that Krasnogorsk bayonets sucks. Why is that?

Because the bayonet requires special lenses, where as the m42 mount was the universal pentax mount that was used in the US but was used heavily in Europe. You can actually get Zeiss lenses in m42.

In the end I know you can easily take out a m42 mount and have someone machine you a different mount if you want.