provided that you want the ETTL system to work on your Canon DSLR camera. The previous canon's flash such as 540EZ or older can't fully work with new Canon DSLR. The only older model still properly work with Canon DSLR is Speed lite 550 EX; however, it's hard to find one now. Flash has a limited time use; the bulb light inside the flash get worn out due to more frequent use. Go for Speed lite 430 EX or 580 EX II. The flash unit is a must when you shoot portrait under the dim light, shadow circumstance, or against the bright lighting background . The internal flash, built-in DSRL, is not sufficient and many cases cast some shadows when using with some Canon lense& hood. Go for DSLR means that you'll spend more money versus the piture quality. So, you be the judge.
A Canon DSLR with its lens cost a lot of money. A Speedlite flash unit will cost you another camera ! So, for Canon SLR users, when you do have to use a flash unit, and cannot afford a Speedlite, what do you use ? Are non-propietary flash units (e.g. those for film SLR)compatible ? What are your experiences ? Thanks.