Could work if the accused has a family to support and a job to go to. Many such live paycheck to paycheck and don't have even the few hundred for minimal bail.
The promise to appear is over the signature of the accused.
Think about a traffic citation.
The driver signs the citation and merely promises to appear in court to address the allegation(s).
The cited driver isn't required to produce anything, other than her/his person as the court proceedings progress.
Many states have allowed persons accused of minor crimes to do this, and the process appears to be gaining traction as other reforms are considered.
As you suggested, electronic monitoring can also be used.
However, most defendants are charged a fee for the monitor, must have a landline (in some cases a mobile phone can work), which fails to address the fact that many people are unable to pay the monitoring fees.
Three years ago in Texas, ankle monitors put parolees at risk of debt and unemployment.
The set-up fee for ankle monitors was between $175 and $200.
The daily fee ranged anywhere from $5 to $40 a day.
That amounted to $35 to $280 each week!!!
Bear in mind that most convicted (released/paroled) felons have great difficulty finding jobs above the minimum wage.
If one is earning $15/hour for a 40 hour work week, after taxes and other mandated deductions, one would be lucky to net (as in take home) $325 weekly!!!
If the monitor company charged $280, the person would have less than $50/week remaining for living, commuting, medical, and other necessities!
I remember the fees because I did (at the time) some pro bono work on behalf financially disadvantaged prison parolees.
I'm sure that cost is much higher today.