I ran my first BQ unofficially running with the pacers. I found it to be a great experience. It took me out of my own head. When it came down to the final miles where everything really counted I either had it or I didn't and I was glad that I didn't waste the first 22 miles of the race fighting off my own pacing anxiety. It largely depends on your pacer and the rest of the people in your group, but typically you'll end up in a group of people similar to you in ability and goals with a pacer who has done faster than your pace before and has some confidence in pulling this off.
The water stops were more crowded, but in the end I found this useful. I noticed that I lost several seconds at each water stop, as evidence by the pacer continuing on without breaking stride hardly at all. It reminded me that I had a few seconds to make up each time and this was easy to do with a pack that just needed to be caught a few meters ahead.
I don't think it's possible to run a marathon with even splits and have done so at even energy. You would need to have a course with no elevation, turns, etc. I laugh when marathoners fight to maintain the same pace every mile. You should be running at effort. Pacers are good at doing this and ones who are familiar with the courses will have smart race strategies. There may even be more than one way to skin a cat, but the important thing is with a pacer you pick one strategy and see it through. In my anecdotal experience the runners trying to hit exact pace starting from mile 1 succeed less often than runners paying less attention to the clock. This is in part I believe because the clock/pace watchers think they need to run a 100% perfect race to accomplish their goal; whereas, the carefree runner is more confident in his or her conditioning, does not require 100% performance to succeed, and will execute a more relaxed effort. Due to the aerobic nature of the marathon the latter runner will almost always succeed more.