When I first rode my new hardtail, I was screaming for bar ends. It had been 10 years since I'd ridden an MTB and riding without bar ends on climbs felt very uncomfortable.
I bought a set, bolted them on, and was happy. Granted, all my riding had been on the roads, but it felt right.
Now that I've started riding trails again, the bar ends have come off. It's all about the geography. Yeah, geography.
When I was riding and racing before, I lived in Colorado and Southern California. Rides there were punctuated by long, continuous climbs. It wasn't uncommon to climb steadily for over 30 minutes at a snails pace. The bar ends were perfect for this with added torque and alternate hand positions.
Now I ride in Georgia. Instead of 3-4 30 minute climbs on a ride, we have 50 30 second climbs with descents and drops in between them. Since I've returned to riding trails, I rarely, if ever use the bar ends simply because I don't have the time or desire to switch hand positions every time the trail pitch reverses.
So much for being retro.