It sounds like they know that your music will make them a good deal more money over time, than they will be likely to pay you upfront.
There’s not a lot of difference between this offer and a WFH deal, except that they aren’t buying the copyright. But, what good is the copyright, if you are giving up your “bundle of rights?”
Traditional exclusive libraries pay anywhere from $200 to $1,000 per cue. What you’re willing to accept is your call.
Personally, I wouldn’t do it.