It seems a reasonable strategy for a company that can take a small hit (relative to their size).
What percentage of first timers need to be converted to regulars to be in profit? I don't know, but even if there's a small loss on this, it's cheap advertising.
Also, I doubt they will offer the free first clean forever. Once that stops, they'll probably have retained at least a quarter of the freebie first timers as regulars, and put their name out there too.
My hunch is that they break even on this part of the business.