I am afraid noone can give you an exact answer to this. Timbers can vary widely even among the same type. Add to that that there are at least four or five types of mahogany, all with different densities and weights. As a generalisation, both mahogany and alder will add warmth and midrange to the overall guitar tone whereas ash is more scooped in the mids.
If you are unsure because you don't have a reference point then the best thing is to discuss with Tim your tonal goals, discuss the exchange policy and make the choice. See whether
a) you like it - mission accomplished
b) you like it but are still missing something - discuss with Tim whether another pickup would come closer
c) you don't like it at all - return the pickup and get the refund - in that case BKPs may not be for you.
Based on my personal experience, scenario c) is highly unlikely.
Cheers Stephan
