Exceptionally large clumps might be a concern, but I'd also be a bit concerned about predictable patterns or general movements of cards throughout the deck.
I think that can be largely eleminated by using cutting and stripping (sometimes called side shuffling).
The new wallet wizard could walk the user (possibly with diagrams and/or video) through this process (even if starting from a pre-determined new deck of cards).
Cut the deck randomly.
Riffle shuffle 1 time.
Strip shuffle.
Riffle shuffle 2 times.
Strip shuffle.
Riffle shuffle 3 times.
Strip shuffle.
Riffle shuffle 4 times.
Cut the deck randomly.
Flip the deck over and record the cards in order into the new wallet wizard.