If it was me and a risk telling me the BF could not be around children, I would want to know WHY. The outcome would likely be the same - he'd be out the door permanently - but I would want to know W.H.Y.
Wouldn't anyone?
Then I'd think crikey, I think I need to take myself off to therapy to figure out why I let a man into me and my children's lives so fast and what could I do differently next time.
But I think knowing why whilst it might not affect the ultimate decision about the BF - it's surely not a natural response to 'he cannot be round your children' to ask well why not! And to be told why - what's the point of doing the risk assessment and not sharing it with the person?
Ok you could take it at face value and say well it must be bad but I don't like doing things based on assumptions and surely it would help illustrate to the OP that she's made (if it turns out to be the case) possibly a poor decision on having this man in her and her kids lives - maybe understanding the details of his past actions and how severely it could have impacted her children, would be a stark learning point that would have incredible value to her. And she'd do things differently in the future. Not ever knowing, only being able to guess, it just wouldn't cut it for me but then I like to have information and make decisions based on information. Any vagueness I would struggle with and in effect, SS have in this case ended up with someone continuing to want a relationship with this person because she doesn't bloody well know what he's supposed to have done! She's complied but what she's waiting for is the reason so she can herself assess if it's appropriate or not,
Given the length of time they've taken with it all she's never actually had an answer for what the problem is so no wonder she's questioning it. This potentially perpetuates a problem, it doesn't resolve whatever threat there is to the OPs children in a finite way - if she closes her CiN case and takes him back, at the very least based on previous performance, the children would be at risk for anything from a long number of weeks to a year before someone noticed and decided that they needed to come back in and see OP again, possibly on the basis of a CP order this time.
However, OP does have options to find out for herself through the two Laws and by taking the matter higher in SS and asking for the final conclusion of the risk assessment, why he's a risk, so she can make the appropriate decisions.