I went clipless (SPD) about 7-8 months ago, and haven't looked back. I was having severe left knee pain back in September / October last year - mostly while climbing or peddling while off the saddle. My Dr. recommended I get cleats and focus on my form, in addition to physical therapy (simply leg lifts, stretching, and such). The combination of these made a world of difference. I still have some discomfort occasionally, but nothing severe. I can now ride much longer with less pain & discomfort.
I haven't fallen (yet), but I've had a couple close calls. One was the typical stop and forget your clipped in - but the other was when my front wheel got caught in an abandoned light-rail track going through a dark parking garage in San Francisco. I had my sunglasses on, and didn't see the track - and of course wasn't expecting it. My front wheel fit nicely into the track, causing me to lose control. Had I unclipped 1/10th of a second later, I would have eaten the pavement.
Practice on a road with lots of stop lights. Make it a habit to unclip about 50' before you get to the stop. Muscle-memory will come in handy when you're faced with an emergency situation (Dooring, etc.). The retention strength of the pedals can be adjusted. Start off with a weak setting, making it easy to pop out, then increase the tension after you're comfortable to make sure you don't pop out unexpectedly.
I went the cheap route - $50 (sale price) for
shoes, and $35 for
pedals. No complaints whatsoever.