I have invested, shortly after it came out, but not extensively looked through it yet - I mainly invested as there is a lot of extra blurb and additional species to the Collins app, both link to each other opening the species up in the other. I saw it as extra reading to Collins which I already loved.
At least some, maybe all? videos are repeats of the Collins, so they are quite nice. The voices I believe may be at least in part or all new?
It is a work in progress that they will add to, and as I have always been intrigued by the paper set, but not the space required to store them, it was a no brainer for me to get it in my collection. Also a lot cheaper.
There are a couple of things still out of date but these are clearly stated before you buy, i.e. distribution and population, but I dare say these may be updated over time if they get enough people buying it making it worthwhile.
I would sum up if you want to add some further detail to Collins, and add some further species, they do work nicely and complement each other - Collins is a must, but BWP is the icing to what I now consider a set.