The name was pretty clear to me, I read it as a pun/play on the verb "to settle", i.e. to perform a financial transaction in order to resolve a debt.
You triggered my curiousity, though: what's your (mis)interpretation? I don't understand the reference to "at home" at all, and basic Googling failed to resolve it.
Another point about their communications is that their main (English) front page copy says "[...] is as easy as pie", an idiomatic expression that to me screams of the US, which was funny because of the European angle.
It seems they're actually fellow Swedes (yay); I've seen some ads for their card reader in local press, too. The reader was then coupled with (if I recall correctly) a phone with a business-type subscription, the ad was by one of the local/Nordic cell phone operators. Interesting.
Well, a Zettel is a small sheet of paper in German. I have no idea if this is the background, but I really read this as iZettel - and it doesn't make any sense.
On the other hand, "Kindle" is something like an angel in German (or a beer), and I think it is a great name anyway!
I always thought it was the bavarian/austrian/swiss diminutive for Zettel. Didn't make much sense to me either, except maybe because an old fashioned receipt is a small "Zettel"?
The problem with this name is that there are several possibilities for pronouncing it... a German "z" ([ay-tse-tl])? An regular English "z" ([ay-ze-tl])? An "s" ([ay-se-tl])?
On the other hand, what the fuck is with that name? iZettle? What's a zettle when it's at home?