I’ve had students do both programs and can offer some insight. Both Pioneer nor Horizon are both ethical and legitimate companies. They both allow students to write independant research papers together with professors. They’re not college consultancies, and they mostly work with sophomores and juniors, so there’s not really any chance that they’d be doing anything untoward with student’s college applications.
Pros for Horizon:
-Horizon is less expensive (about 5k versus Pioneer’s 7k)
-Discloses who the students’ professors are before they ask them to apply and pay a tuition fee
-Horizon has the same number of class hours in the program as Pioneer, but they also have a Teaching Assistant who works with students for an additional 6 hours throughout the program.
-Horizon gives admissions decisions much faster than Pioneer (probably because they’re smaller)
Pros for Pioneer:
-Pioneer has been in the research space for longer than Horizon (~2012 versus 2016)
-Offers more topics
-Runs their own journal (not sure how meaningful publishing in that journal would be though?)
That’s my 2 cents at least.