The Apollo™ half rack has a flat foot base that stabilizes the rack when doing dynamic movements, so you don't need to bolt it down to the floor.
With the PR-5000, if you add the Rear Base Stabilizer onto a 41" depth configuration, you don't have to bolt your rack down. However, if you're using the Iso Arms, Spotter Arms, or Globe Grip Pull-Up Bar, you do need to bolt your rack down, even with the Rear Base Stabilizer, regardless of your rack's depth. With those attachments, you also need to add Front Foot Extensions to keep the rack stable.
The Omni Rack also has a flat foot base. However, the Omni has a bigger footprint than the Apollo™. The Apollo™ was designed to take up minimal space without compromising your workout. It's almost as compact as the PR-1100, but with extra stability and compatibility with many more attachments. The Apollo™ works with all 5000 Series attachments except for the Belt Squat and Ares Cable Attachment.