Hi All
The first thing you need to remember is that the 3 jacks in this thread they are designed for different uses
the standard hydraulic bottle jack is ONLY designed to be used on a solid, stable, level surface( concrete, bitumen or very hard packed dirt), so if you don't go off road this is all you will need, a bottle jack can be very unsafe when used on sloping or soft ground!.
The exhaust jack is designed to be used in off road situations where the surface is SOFT, sand, mud and snow, BUT they are very prone to puncture from sharp objects( yes they have been improved in recent years), but you need to be very careful with rocks, sticks, sharp points on your vehicle( welds etc), and be very careful of the exhaust pipe it will melt through an exhaust jack in seconds.
Hi-lift jack is designed for off road, can be used in all off road situations, you need good solid lift points or one of the many accessories now available, yes they can be unsafe if used with out care, but if you learn how to use them correctly, they are one of the most versatile 4x4 accessories available.
as some have already said they ca also be used as a hand winch
For me going off road with out a Hi lift jack is asking for trouble, like all things if you service and maintain them they will give you years of service and will get you out of those sticky spots when all else has failed
my 2 cents worth
Cheers yoda