I'm a die-hard lefty and have had at least 1 AR for the last 11 years... All I have ever "needed" is the ambi (actually reversible - from Olympic Arms) safety and an ambi-catch. I didn't like the "ambi" safety because the "left" side safety is under my fat trigger finger when I fire, and it's just annoying. The Oly Arms model has the safety groove in both sides, so you can use it from either side (why didn't the Army think of that?)
If I had to choose only one, I'd still "need" the safety moreso than the ambi-catch, but since I don't have to choose, I sure as heck won't be selling my ambi-catch. That's one thing you'll notice... you never see an Ambi catch on the EE for sale used... That's a pretty good sign that either NOBODY is buying them, or EVERYONE who buys one keeps it.