Can't say that this was solely the result of the sprayer, but I used it on a 1.050 wheat I made last Friday. Sprayed the wort into the fermenter with the sprayer, didn't shake it at all, and pitched a small starter. It was going like a rocket less than 12 hours later and there's no estery or other off-odors coming off of it. My gut says the sprayer along with a healthy starter is fine for low-grav beers.
The sprayer is a good gadget to have, that being said i still do some shaking. I don't go throwing my back out or anything but a solid shake, the sprayer, and a yeast starter last saturday on my american hefe had that thing absolutely erupting.
I also like the sprayer because it helps dissipate the star-san foam in my carboys so i don't get huge foam-snakes as often.
also, the sprayer can be used as a makeshift sparger if you ever move to all-grain!
However, If I was only pitching a single Wyeast smack pack or white labs vial, I would pitch after shaking. That way, all the yeast ends up in the beer instead of coating the sides of the carboy.
I now use yeast starters, but still pitch after the shake.
I saw a chart here somewhere that said a siphon sprayer will give 4 ppm of oxygen. With that in mind, will siphoning twice give you the preferred 8 ppm? Or just give only a slight increase? Just a thought to ponder.
I found that when using liquid yeast, even with correct pitching rates and a stir plate, proper oxygenation made a huge difference in the finished beer. By proper oxygenation, I mean 60-90 seconds of pure O2 in a 5 gallon batch, which has been tested to provide ~10 ppm in a typical wort. Starters are certainly a must, but they are too small a volume to carry enough O2 through to the fermentation.
On the other hand, it seems like if using properly rehydrated dry yeast, oxygenation is not nearly as important. According to the manufacturers, O2may help, and certainly won't hurt. I can't really explain why, but it may have something to do with the energy stores the yeast manufacturers have built into the dry product. In other words, if a sprayer/shaking can get you around 5 ppm, that may certainly be enough for dry yeast.
In my experience, liquid and dry yeast are different animals, and the handling requirements are much different.
In the past year I started trying to force 02 into everything, starter, wort before adding starter and after adding starter. It has made a big difference. I have not had a start very active fermentation in less than 6 hours after pitching and have not had one be in active fermentation more that 72 hours since I made to the change.