It turned out that Bristol GS has both ATPL Online and BGS Online as question bank.
BGS does not have two question banks. Until about a year ago BGS worked in conjunction with a software company (I think it was called IDC). Together they produced the ATPL Online question bank.
Until the break-up ATPL Online was generally recognized as being the best thing on the market. Whether it has remained the best is a matter of debate.
The two companies then went their separate ways and the software company took ATPL Online with it. As far as I am aware BGS no longer play any part in the running of ATPL Online.
A few months after the break-up, BGS produced their own online question bank. If you want to read comments made by current users go to the bristol.gs website, select Resources then ATP Forum, then read the posts in the BGS Online forum.
As far as I am aware neither the ATPL Online providers nor the Aviation exams providers have a similar open feedback forum for potential customers to read. BGS should be commended for their openness.