I think TCredits is the best gift which can be offered to any PSA or CSA. The reason is that they can be used immediately whereas if you gift them $1 then they can't use it until they have $7 in their account.
Also, if you want them to grow in SFI then you should gift them TCredits because this is one of the best things SFI has provided all of us and is the reason for huge success for many SFIers.