The advantage of hand magnifiers is that they are portable and will slip into most handbags or pockets. They are relatively inexpensive, socially acceptable (people don't usually mind using them in public) and they are available in a wide range of powers (from 1.5x to 7x).
The disadvantages of Hand Held Magnifiers are that every time you pick one up you lose the use of a hand! It is difficult (though not impossible) to write using a hand magnifier, but if you have a hand tremor then it may be difficult to keep the lens in focus. A very useful accessory for any hand magnifier is a Double Ended Clamp.
This clamp consists of a flexible arm with a large "Bull Dog" clamp at each end; one end is clamped to the handle of the magnifier and the other to the edge of a desk or table. It can hold most magnifiers at the appropriate angle, thus allowing both hands to be kept free.