What is one disadvantage and one advantage of a car jack?

Advantage: portal light weight jack that is highly maneuverable.

Disadvantage: slightly unstable and takes a loooong time to jack a vehicle.

End result: use it if it's all you have, but place something under the car as you jack in case it gives out (like a spare tire if your changing one) so it doesn't crush you if it falls. But, a mechanics shop floor-jack is best. Fast and easy to use with little to no effort.

For continual car work, floor jacks can be cheap. They go by tonnage, so a cheap floor jack can lift 1&1/2 tons and is around $35-$50. A bigger jack that can lift more is more expensive and also heavier.

Check places like Auto-Zone, Pep boys, Kragen, O'Reilly, and Walmart.