Others will disagree but I think you made a good choice.
I have a DPMS GII Hunter and I am impressed with the rifle. The rifle is sub-MOA and is reliable as can be.
If your rifle has very few rounds down the barrel, I suggest to follow the suggested break in procedure mainly because I followed it and the rifle became smooth and accurate.
I used quality USA manufactured military styled(147grn) ammunition to do the break in. I also ran the rifle wet.
I also installed an adjustable gas block because my rifle was way overgassed. I think you will probably want to do the same.
I don't know which DPMS rifle you purchased but the GIIs have a problem with magpul mags. The problem is the bolt hold does not raise enough to consistantly hold the bolt on an empty mag or it just barely holds the bolt causing a lot of wear and tear on the hold itself.
If the rifle is not a GII, no worries. If it is, one can easily find the fix on the internet.
My rifle and my sons rifle did not shoot well with the 147-155grn type slugs. 165-168grn slugs were the favorite of our rifles.
Good luck with your AR-10, there is a reason they are called big boys Barbie dolls, you can dress it up any way you would like too!
Have fun and shoot straight.