Bgsonline is helpfull, though in the more extensive subjects it is not enough. I mean, BGS has less questions then Atplonline and way less then AviationExam.
I got screwed couple of times because never seen the questions before. Though I did also studying in the books, so not only studying by Clicking. So atleast I scored ok because of book knowledge. But If I didnt had that, then I would have scored much lower. And I use Atplonline. Which does ok. But I miss explanations by many questions. Same story at BGS. I have passed almost all the Atpl exams, so aviationexam is not usefull for now, but since you have to start studying I suggest you to take aviationexam. Don t safe money on you study material on the total training costs. Invest in good marks by having the best mamterial you can get.