What's your experience with property management co's? Worth it?

Me and my business partner have been investing for 2.5 years. We have built up cash through flipping houses and in the past few months we have purchased 2 separate properties with 8 rental units in Columbus.

We both work full time in unrelated fields, have families, etc. we are strapped for time with jobs and flips. I KNOW we cannot add more time consuming work to our plates.

1. What's been your experience with property management companies...likes/dislikes, etc.

2. As we look for a company what are some things to look out for - mistakes you've made - perks that are totally essential in your opinion? (no vacancy charges, no new leasing fees, online management portals, etc.)

Thanks