If you don't provide the (external) client a QV license (e.g. a leased Named CAL) from your company's pool of licenses, I don't see anything that would be against license agreement.
I am assuming that the QVW itself (and the data contained therein) isn't violating any legal agreements with 3rd parties / copyrights.
Remember that opening your QVW in the client's unlicensed desktop version will consume a so called recovery attempt.
Though this shouldn't be an issue when looking at a single QVW / client machine, there are some reported issues with personal edition stopped opening a QVW (reporting max number of recoveries reached).
Also if you want to provide some updates to the QVW, this might be getting an issue.
As an alternative, if your client is a candidate for a new Qlik customer, you can ask Qlik for a temporary test license, something they have done in the past to support so called SiBs (Seeing is Believing, kind of a demo at customer's site).
.png "Luminary Alumni"){kind=icon}
