No horror stories - just good things. I use it on my T1i, and it has provided me with a number of features that the native Canon firmware doesn't. The ones I use routinely is the spotmeter (customized readout); customizable-under/over exposure indicator; the intervalometer; various info displays; fine controls on ISO, shutter speed, white balance; many options for customizing Live-View, etc. For instance, I have my ML spotmeter set up to read the spot and give me a reading in the 0-255 range. Anything in the 240+ range is essentially going to be blown out, anything in the 0-10 range will be blocked. This allows me to adjust the exposure so that the highlight is at the 240 range - and I then know that in the output image, the highlight will be with detail. The histogram doesn't help as much if you have areas of the image that you don't care about keeping the detail in - those will show up on the right side, but won't give you an indication if your chosen highlight is at the 255 level or not. Recently, I used the intervalometer to set up a series of shots at night that I wanted to use to make star-trail images - no additional hardware was needed. I also used the customizable LV features to allow me to see what I was shooting under very dim conditions where flash was going to provide the actual light for the subject. So my take-away is that you'll have a lot more options available to you to learn, and once learned, will help your photography.