It's a truth universally acknowledged that everyone loves getting stuff for free. Unfortunately, there's no such thing as a free smartphone, no matter how alluring that "$0" handset repayment fee is. This is made abundantly clear when you compare a SIM-only plan to a 24-month contract, even before you factor in any handset repayments.
However, we tend to see the first plan where a carrier drops the handset repayment fee as a sort of tipping point. If you're paying a handset fee there's a chance you're paying too much for your phone. If you're paying $0 for the phone, you could be paying too much for data. Sometimes those first $0 handset repayment plans can be 'just right' if you're looking for the best value option.