This is especially true for higher-ticket items like silver jewellery, where I'm not likely to have $60 kicking around in my pocket, but I'll have no problem putting $60 on my Visa. Personally, I also find it hard to part with $60 in cash (more tangible) vs. putting it on my Visa or debit card.
For actual businesses (like bigger food carts), a proper 3G bank terminal is probably the appropriate response, but in places where people aren't likely to expect any card use at all (smaller food carts, craft fairs, yard sales), having Square (or similar) is a net positive.
Square is a godsend for small businesses there. Square's all over Portland, for instance, not just at yard sales and craft faires but in real businesses because it's an absolutely disruptive form of payment that lets them avoid some onerous fees and setup costs, and it lets them accept debit because debit piggybacks on the credit system in the US.
But it's pretty crippled for that here in Canada. I know several small business, including my wife's, who were dying for Square to come here, because getting set up with a proper payment terminal in Canada is obscenely expensive for a small business.
But there's absolutely no way that they could use this as offered, with zero debit support, ubiquitous customer demand for debit usage, and no support for chip-reading in an environment where chip usage will be mandatory in 2 years and in which not using a chip already causes credit card transactions to be declined as 'suspicious' at a fairly high rate.