I honestly went right to SD retics from ball pythons. Granted I researched and weighed my pros and cons and such for about two years before pulling the trigger. Don't know that I'd say they grow slower than mainlands though... Phyllis went from ~56grams and 20" to 8.5" and 10+ pounds in 20 months. She's an absolute beast of a super dwarf and she's 100% SD. She is super interactive, inquisitive, never misses a meal, and is an absolute joy to work with. I'd be happy to talk about my experience with her or Gerald, my 50% SD male Ultra Ivory if you're interested in knowing more. Both have their own progression threads on here. I've had Phyllis since she was three weeks old and Gerald was about a year old when I got him. They're significantly more work in maintenance and upkeep (read: daily piss cleanings) than a ball python but I love 'em and wouldn't trade them for anything.