I've owned the Airflex for a year now and it's a massive step up from the Ninja.
Bigger fresh water tank and waste tank, never have to take it upstairs and have run 100 feet of hose from it comfortably. The third vac leaves the carpet considerably drier than a twin vac.
I have to load mine into my van on it's back due to the raised floor on my van. I wrap the leads around the handle, remove the gate valve bend, put the handle wheels onto the van floor, lift the machine up slightly above horizontal and slide the machine in. It doesn't foul anything on the way in.
As far as emptying is concerned, I always have a towel on the floor under the gate valve anyway. It really isn't an issue emptying into a bucket - as for the bucket getting heavy, I think you need more shredded wheat for breakfast
I tilt the machine back to get the last dregs out of the waste tank after I have rinsed it out, again this isn't a problem.
I haven't used a Scorpion or an Alltec triple vac so I can't compare - but the Airlex works just fine for me and is backed up with good customer service.