I have both Dums and ball pythons. From strictly a husbandry standpoint I think Dums are a better choice for the first-time keeper. They are kept a bit cooler and dryer than ball pythons so they're more tolerant of the husbandry mistakes new keepers are likely to make. They're also not picky about eating - mine all take frozen/thaw rats or rabbits.
They eventually do get bigger than ball pythons BUT it takes years for them to grow up so you have plenty of time to learn how to deal with them as they grow; they're not mainland retics that get up to ten feet long in their first year. My oldest male is five and is just barely six feet as of this year.
They're also very docile and accept being handled very quickly, though you do have to be careful in that they are extremely strong for their length. As a ground-based species they're very thick-bodied, and they like to feel well-supported when being held.
They also love to burrow so if you keep a youngster on aspen or cypress, offer a few inches of it. I don't dump a foot of substrate into my adults' enclosures though, they get an old towel to hide under.