You need the likes of OATS and BGS to get you through the exams. Anyone thinking that the day you pass your final 14th exam is the day you stop learning needs their head examined. No course is going to equip you with everything you need to know to pass interviews, or allow you to have a long conversation with the guy who designed the hydraulic system on a 757.
I did BGS, and I got through all of my exams fairly easily. I've no complaints with BGS. But, I've found myself reading through numerous books on various technical subjects since passing my ATPLs. I made many mental notes to re-visit topics when I was studying - but at the time of my exams all I wanted to do was pass.
This was nearly 10 months ago. The subjects are so vast and interesting (well, some of them) that you will build knowledge gradually over the coming years.
I would canvass opinion on BGS, OATS and GTS - all of whom have good reviews.