I took both this year. I trained at a historically DO peds program that was dual accredited by ACGME and now just ACGME due to the merger.
My program paid for the DO exam which were supposed to be in spring 2020 and they got rescheduled to October because of the pandemic. I treated the test as a practice exam 2 weeks before the ABP.
The DO test is very horribly written and outdated. I think worse written than even comlex. The questions are more straightforward, mostly 1st order thinking of either you know this fact or don't. Not a lot of critical thinking. The OMM questions were weird but admittedly I didn't study much for that and just looked at old OMM reviews from med school for a few days before the test. Definitely much much easier than the ABP.
I took the test mostly because it was paid for and gives me a safety net if I fail ABP, I'm still board certified. I don't plan on ever renewing the DO board certification ever.
So I recommend if you are eligible for it, which I imagine you are since there's no such thing as DO residencies anymore as all had to get acgme accreditation or close, take the ABP instead. If you are not a good test taker or fail the ABP you can look at the DO boards as a backup.
For studying I used PREP questions which were good to review the content. I also did medstudy Qbank. The medstudy Qs which were written more similar to the actual ABP exam imo compared to prep. For content review I used medstudy books and videos.
I also had gotten a trial of the NEJM qbank through my residency program and did like half of that qbank for extra practice. But I didn't think it was as good as medstudy or prep to prepare.
Hope this helps!
