And finally, you've got to make sure you've got enough speed to hit a long iron.
If you think these clubs don't have an awful lot of loft on them, plus they don't have a big sole so they're not as easy to strike and there's not as much weight at the bottom of it like a Rescue club.
You'll see that Rory McIlroy can hit a 3-iron no problem as he can swing his driver at 125mph if he wants to. Average Joe swings it more like a Ladies European Tour pro if they're lucky at around 30mph slower than Rory. If you looked at an Ladies European Tour player's bag, normally you'll see a lot of hybrids in there.
Providing you're fast enough to get the ball at its peak height, then absolutely go for it with the long irons.
If you're not blessed with speed, however, I'd stay away from them. It's just not worth it, unless the golf course you play requires a low penetrating ball flight. They are hard to get up in the air and the strike is not as forgiving. That's why the hybrid is such a popular club these days as you don't have to have as much speed to get the ball in the air.
With the long iron, like a 3 or 4-iron, you've got to be fast enough, control the low point of the swing and hit the middle of the club to get the most out of it.