I think this is a clever use of the HR+ feature.
I was curious to see the response time and I remembered another forum user @Gbonhommd posted a similar concept workout 1-2 weeks ago: [SOLVED] - HR Targets not working after erg segments in custom workouts - #48 by Alex
I grabbed a screen shot of his data and added a few lines.
The response time is pretty good in my opinion. Power response will be down to each individual user.
Dave