Hey Blue!

I have not attended either type of program. I cannot give you first hand experiences.

I have had a couple of close friends do both types. They'd found the PHP more intensive, of course. This was a good choice when they were in severe distress and really needed help with being safe during most of the day.

The IOP had allowed them to work some each day.

Both programs were for psych and/or substance abuse issues.

I have a copy of the extensive manual used in both PHP and IOP. The manual is so large they could not cover all of the material.
They were taught mostly DBT, CBT and Mindfulness.

They had found they did have a lot in common with people attending for substance abuse. All were seeking coping skills.

One of your considerations might be whether or not your insurer covers both types of programs.

Think carefully about how you'd like to handle any choice re: your employer.
One of my friends talked with the intake person re: attending. She had filled out the forms and had emailed them to the intake person, as directed for the interview.. My friend was still considering her options. The intake worker contacted her employer's personnel department, disclosing everything needed to gain approval for "leave" in order to attend PHP. She was going to need medical leave in order to attend. She had NOT authorized the intake worker to schedule leave with personnel.

In some cases, people take vacation time. Others are able to work and attend IOP. In this cases, there is no reason for personnel to get involved.(as far as I know.)

I am glad you're looking into these options.