Thanls a lot for taking your time to write this awesome comment!

The thing is we have very little control over the checkout area, since it is hosted by our payment provider and we cannot run tests there. We are not happy about it and we will move to Stripe as soon as it will be available outside of the US.

Really, thnaks a lot for this. I will look into this right now, maybe we could fix some of those.

EDIT: We've removed the quantity field from the SaaS products, never thought of that before, thanks.