Yes, we can consider krakex app as a good app for jee main and jee advance preparation as well. It consists these qualities:-

(1) Developed by IIT alumni which is a great thing in this app you will get short tricks and methods which iitian use for jee examination.

(2) It contains previous years question paper with detailed solutions, which is very important for an aspirant to understand about the nature and pattern of the questions asked in previous year.

(3) It is a personalized learning app. But it needs some more qualities like mock tests and others.

Harshini, if you are looking for online JEE Mains preparatory course, we have Knock out packages. They are affordable and they have concept based videos, mock tests. The classes are backed by AI. Have a look at the packages at our page: https://learn.careers360.com/engineering/jee-main/