We use our spinnaker pole to pole out our jib all the time. We don't have a separate whisker pole, and our biggest genoa has an LP of only 135% of "J."
How long of a pole you want will depend on what size sail you are trying to pole out. A spinnaker pole is usually limited to the "J" dimension of your sailplan, which generally isn't long enough to give you good shape poling out a 150% genoa, but works OK with a 135% genoa. Poling out the big genoa is where the adjustable-length whisker poles typically have an advantage (although if you're planning to do any racing, check the restrictions that come with your handicap rating).
Our new spinnaker pole is carbon fiber with composite ends and spectra bridles, so it is very light. I'm not sure how an adjustable-length whisker pole could be any lighter... (Our old aluminum spinnaker pole was a monster, though).
This is a 150% genny and the photo is in light conditions. Later that day, the wind picked up to 20-25kn. I use this genny instead of a drifter/assymetrical when I am expecting the breeze to pick up and I can reduce sail area by furling with ease as the conditions change.
I often use a snap shackle ( a huge one) in order to be able to release the spin pole whilst under a moderate amount of pressure if this is what is needed. Other times in heavier conditions, I use a third sheet.=> the real meaning of the saying "3 sheets to the wind".
I also have a smaller pole (about 3.3m) with a double purchase block. This is used for the inner jib (wing and wing style) or to raise the dinghy or anything heavy onto the deck .
You can use a spinnaker pole, but it won't hold the sail out as far as a whisker pole. You can sail wing and wing without a pole, if there's enough wind. In light air, the sail will collapse without a pole, or with a pole that's too short. I have found that it's much more difficult to sail wung out without a pole with a boat that is fractional rigged. It can be done, but it's a struggle.