Shooting TTL, while undeniably convenient, is analagous to shooting with auto white balance. Most of the times the camera will make a pretty good decision, but there are times when it won't ... and potentially worse, sometimes where it will, and sometimes where it won't (some overexposed, some underexposed), meaning simple batch processing of all photos is impossible, and each photo may have to be post-processed individually.
For fast-paced shooting, I use a 580EXII either on camera or handheld with an off camera shoe cord. Though I am sure the vast majority of the cheaper flashes are safe, in general, I feel slightly more comfortable with a genuine Canon flash attached physically (either hotshoe, or off camera cord) to my camera.
For shots where one has the time to set the shot up e.g. on set, multiple lights etc., I use cheap manual flashes & cheap RF radio triggers. Helps keep the cost down, and results are usually more consistent when using manually set flashes. Not necessarily perfectly exposed, but when not, it's more likely that batch processing will be a possibility. I have 2 genuine Canon flashes (for my 2 Canon bodies), and 4 cheap manual flashes, and 2 cheap RF master radio triggers (1 spare, or for use on 2nd body when using a dual body setup), and 4 cheap RF slave triggers for triggering them. When you want/need multiple flash heads & RF triggers, especially when you are shooting for fun as a hobby, not for pay, as I am, using cheaper manual flashes & RF triggers can mean substantial savings (or a more expansive setup for the same money). Having a different system from someone else can be an advantage, since they may use different frequencies, thereby resulting in less interference / accidental triggering if there are other photographers in the area. However, it can also be a disadvantage if something breaks or is left behind, and you can't lend to / borrow from others.
