That's a tough question. It's so hard for anyone to measure the quality and effectiveness of an IELTS course objectively unless they've taken all of the IELTS courses available!

So here's a quick checklist of things to look for in a course. Go to the blog to download the checklist; I designed it to help you make an informed decision. 

https://ieltsetc.com/2021/11/best-online-ielts-course/