Here's a scenario where extended ramps would come in handy. Let's say you've got a high round M4, a real M4, not these toys that everybody posts pictures of here
, but the real deal. Due to it's high round count, the gas port has eroded open a little and this M4 cycles pretty fast. Additionally , this M4 has had hundreds, if not thousands of magazines that have been inserted and ejected out of it and this has worn the top of the mag catch a little, which drops the magazine down in the magwell. On top of this, you are using an old, worn USGI mag which has a weak spring. The worn mag allows the mag to sit even lower in the magwell, due to wear at the mag catch area. The weak spring cannot push rounds up as fast as it used to.
This combo will give you a super fast cycling carbine, with magazines sitting very low in the magwell, which puts the bullet tips farther down in relation to the feed ramps. Add a weak spring that cannot push up rounds fast enough to keep up with the cycling rate and you have a possible need for an extended ramp to increase the odds of a bullet feeding.
If you fall into the above situation, you
need extended feed ramps. If you don't, extended ramps will certainly not hurt you, but you shouldn't pay any more to get them, as they probably aren't needed. If you choose to get extended ramps, I recommend you get the proper equipment to get them, rather than hacking them into existing equipment. YMMV.