I am using k4 note from more than a year it worked fine.i did not face any major issues after using this phones.The genuine weaknesses of the phone that I found: -
1) camera is mindblowing in outer lighting but in low lighting it is not that much good.
2) it generally heats up even on normal usage or while charging but the phone is durable and can easily handle the heat so heating is not going to harm you and your phone anyway.
3) lenovo gives slow updates.updates in lenovo are rare.now a days lenovo is providing updates very late and very rarely.this is a major issue.