MiG-21, just as any complex piece of software, has some issues. The navigation system could be better, weapons selector is inaccurately implemented, gunsight needs some improvement too etc. I don't have a clue how a MiG-21 is supposed to behave in flight, so I won't comment the flight model.
But I would dare to say that none of these issues, no matter how annoying some of them may be, are not even close to be game braking, and don't make MiG-21 a bad module. On the contrary, it is a great module.
Recently, after the LNS split, Dolphin said they are intensifying the work on the module. Indeed, there seem to be more activity in their bug tracker during last month then in the entire 2016 :). So let's wait what will the future patches bring. I know I'll continue to enjoy the MiG just as the day I bought it almost two years ago, and will continue to recommend it to anybody who asks.