In fact a parallel kangaroo program that look for a single key creates several pubkeys from this key (by simply translating it). So this is a multi key search but this does not decrease the probability to solve this single key. It just allows a simple parallelization.

Usually, for a multi target attack, the first key has no benefit but the following keys can gain from the previous calculation.
If you want to search a pubkey with a x starting with 32 leading F (between n and p), you will have to perform ~2^128 group operations.