ambiguous?

[Bridget]

Would would you use?

Customers should hold onto their savings during this crisis.
Customers should hold on to their savings during this crisis.

[jirikoo]

Would would you use?

Customers should hold onto their savings during this crisis.
Customers should hold on to their savings during this crisis.

I wouldn't say ambiguous, rather irrelevant in this context and case. Both are correct in my opinion. But there are some little differences in structure and a little in terminology.

Lets examine the verbs for a moment:

Hold onto is a transitive (inseperable) phrasal verb with the direct object "their savings during this crisis"

Hold on is also a phrasal verb, however intransitive with a prepositional object "their savings during this crisis"

[OddThomas]

Hold onto may appear in written use, but I wouldn't accept it as a standard phrasal verb. The customary verb is hold on, and to is the expected preposition. In speech, of course, the issue never arises.