I currently fly a variety of airplanes that have 2-5 point restraints. All of them are equally good at keeping my head from hitting the ceiling/canopy during turbulence, if worn correctly.
We talked to all the harness manufactures at Oshkosh this year before making a purchase for our RV-8. All of the manufactures gave me the same story: The difference between 2, 3, 4, 5, 6 and 7 point harnesses is in crash protection. The primary purpose of the crotch strap is to keep you from slipping under the waist belt during a crash. It keeps your hips in place and prevents the belts from sliding up over your stomach and causing internal injuries. Granted, the more points of restraint you have, the better you'll be restrained during turbulence, but that's a side issue.
Five of the planes I fly have a traditional buckle where you thread the shoulder and crotch straps over the tongue before latching it into the female side, so you have to get all the belts to cooperate at the same time. It's not uncommon for me to drop on of the straps while I'm reaching for another one, and I have to find it again and thread it back through the tongue. The traditional buckle is a little more cumbersome than a rotary buckle, which normally allows you to insert one strap at a time, but in my opinion it's not significant. The rotary buckle is more expensive. They both work well at keeping the belts in place, and both can be released in a single motion.
You'll have to decide if the convenience of the rotary buckle is worth the increased price. You'll probably get used to whatever you decide to install and it won't be an issue.