That is rated to 5,000 lbs, so you would already be at it's maximum safety limits.
I personally wouldn't get under a vehicle being lifted like that, and the weak "safety" lock they have if the hydraulic cylinder fails.
Just my 2 cents.
According to Toyota, the curb weight of the 4Runners is as follows:
SR5 - Curb weight (lb.) 4400
Trail - Curb weight (lb.) 4750
Limited - Curb weight (lb.) 4525
TRD Pro - Curb weight (lb.) 4750
Also, I think these units are heavier duty than you may be thinking. I am going to try to find a local distributor so I can go get my hands on one.
One of the specific claims they make is "much safer than jack stands" so we'll see.
Edit:
Also, in March 2016 they are coming out with a BL7000 which will easily exceed the curb weight of most street SUV's/Trucks.
"Is the QuickJack safe?
If you compare the number of people killed or injured annually using floor jacks or jack stands to other car lifting solutions, it’s evident that the QuickJack provides increased safety when installed and operated properly. Información en Español, clic aquí."
Personally I always overkill safety if I am going to be under a vehicle - ergo I would still have jack stands, concrete blocks, etc.. under the car if I am physically under it. Being crushed to death is not the way I want to exit this world.
