no known negative effects yet. But Caribdis' last game had a pair of seemingly inconsequential decisions lead to bad ends. So it's totally within the realm of possibility for it to have negative effects down the road.
Consider it a flag. It is not known what result this decision will lead to. It can either save someone in the future, or lead to negative consequences.
If you have read to the end of the current version, you may have noticed how the purchased trinket helped in a certain situation. If I explain in more detail, it will turn out to be a spoiler)
Also, there we have is very low possibility that Cari himself did not come up with why he offered this to us :D