The jack supplied with any car should be used for emergency flat tire change out only. And never even put anything of value (including your head) under the car when supported by the jack (ANY jack) only....if it goes there will be NO warning.

Indeed the jacks supplied with the 240 series were a cruel joke - Volvo screwed up in the past too!! I bought a nice 2.5 ton scissor jack for like $15 that is better than any supplied jack to replace the 245 piece of sh%t.

If you do ANY car work, even rotating/changing to snows yourself, a hydraulic floor jack and some jack stands is a very worthwhile investment. I mean you just spent over/around $30,000 for a car...Is about $150 too much to protect your life/limbs?

Now to address your questions - the 850 jack (haven't seen the S70 jack) seems really funky, but no more dangerous than most. To tell you the truth I've never had to use mine because I have a floor jack and the one time I got flats it was both left tires so I had to call for a tow anyway (one spare)!!

As to the one slot to jack one side up, I think it works great - 3 Ton floor jack under slot, a couple pumps, car up, four (yes 4!) jack stands for saftety, shake the car hard to make sure it solid and it's off to work...